Tag: asteroids

Meet Gault the Oddball Asteroid

In October 2018, sky-watchers saw a dramatic change in Gault’s lazy swing in its orbit: it had brightened all of a sudden.

Using terrestrial and space-based telescopes, astronomers recently turned detectives to confirm an unprecedented discovery: an asteroid spinning so rapidly that it is literally coming apart at its seams. Telltale images of the asteroid Gault shot by NASA’s Hubble Space Telescope show two long ‘tails’ of dust trailing the space rock. These images, scientists say, are definitive proof that Gault is slowly breaking apart.

Asteroids don’t disintegrate often; the mechanics of those that do are still hazy for astronomers. Icy asteroids simply sublimate – change directly into water vapour – as they near the Sun and literally melt away. In the case of rocky asteroids like Gault, however, there are two ways they can disintegrate: two asteroids could slam into each faster than a bullet and pulverise themselves into dust or a roid could rotate so fast that it steadily loses its rocky mass and crumbles at some point. With the four-kilometre-wide Gault, scientists were not sure what was going on – until now.

Ever since it was discovered in 1988, Gault has been just another faint, stony asteroid in the main asteroid belt between Mars and Jupiter, which is home to over 800,000 known asteroids. In October 2018, sky-watchers saw a dramatic change in Gault’s lazy swing in its orbit: it had brightened all of a sudden. On closer study using NASA’s Asteroid Terrestrial-Impact Last Alert System (ATLAS) and the Panoramic Survey Telescope and Rapid Response System (PanSTARRS) telescopes in Hawaii, scientists were astonished to see that Gault had sprouted a thin dusty ‘tail’ that streamed out for hundreds of thousands of kilometres.

Also read: An Asteroid From Another Star System Just Zipped Past Our Sun

Most asteroids usually appear like tiny points of light and don’t have tails of dust trailing behind them. Tails are usually associated with comets when their orbits brigs them near the Sun. However, comets hail from the outer Solar System and are in Earth’s ‘neighbourhood’ when their eccentric orbits around the Sun bring them closer to us.

As they near the Sun, some of the ice on the comet’s surface vaporises and is ejected into space in a direction away from the Sun, visible as the tail.

However, scientists were in for a bigger surprise when, earlier this year, European and Canadian astronomers discovered a second debris tail behind Gault. Around the world, telescopes like the ATLAS in Hawaii along with the William Herschel Telescope in La Palma and the European Space Agency’s Optical Ground Station in Tenerife, Spain, turned in unison to focus on Gault. Indian scientists played a key role in working out the actual details of how Gault temporarily morphed into a ‘comet’. Astronomers at the Himalayan Chandra Telescope in Hanle, Ladakh, discovered that Gault had a rotation period of two hours – the critical speed at which asteroids usually start to break up.

So what makes Gault such an oddball asteroid? Did it have a close encounter of the roid-kind with other space rocks so that the collisions caused a sudden eruption of dust particles and produced the ‘tails’? But an asteroid impacting another would cause a big plume of dust to billow into space, and no such event was captured in any of the images taken by the Hubble space telescope since last September.

Astronomers are now more or less united in believing that the only way to explain Gault’s disintegration would be to consider the YORP effect. YORP is an acronym for ‘Yarkovsky-O’Keefe-Radzievskii-Paddack’, four scientists who promoted this theory in the 19th century. When heated unevenly by sunlight, infrared radiation from an asteroid’s surface escapes – along with some of its angular momentum. This creates a thermal torque or spin that causes the roid to rotate faster. As a result, the centrifugal force soon makes its surface unstable, sending dust and debris drifting into space.

Also read: Space Subjects That Will Get the World’s Attention in 2019 and Beyond

Active asteroids like Gault are uncommon and scientists have been able to catalogue barely 20 of them so far. But with advanced telescopes like the PanSTARRS, astronomers can now look more closely at the asteroid belt and spot active space rocks from the dust they leave in their wake. As for Gault, its spin to death is a grim reminder of the unpredictable behaviour of asteroids and the potential threat they hold for Planet Earth.

Look at the so-called “minor planets” of the main asteroid belt: they range in size from Ceres – at 950 km across, the largest – to small pebbles. Some of them have eccentric orbits that bring closer to the Sun than Mercury. Such peculiar orbits inevitably also bring them quite close to Earth. Hermes, a binary roid, holds the ‘nearest approach’ record among large asteroids. It zoomed past Earth at less than 643,600 km in 1937.

So knowing more about asteroids – especially active ones like Gault – and how to approach them could be useful one day if Earth is ever threatened by the ultimate cosmic horror story. For all we know, a runaway asteroid somewhere out there may have our fragile blue-green planet in its crosshairs as it careens through space.

Prakash Chandra is a science writer.

Did You Know? On Average, Mercury Is Earth’s Closest Neighbour.

Trying to improve stargazing and space-journeying are lofty goals but we often forget that pursuing and celebrating curiosities are valuable, too.

Which planet is closest to Earth? Common sense suggests it’s Venus or Mars, and common sense would be right. However, technically speaking, this isn’t entirely true. At different points in their respective orbits, Earth, Venus and Mars are at different distances from each other. Out of curiosity, if these variations in distance were factored in, which planet would be closest?

The answer is weird: it’s Mercury.

Point-circle method (PCM) is a technique that averages the distance between every point on a planet’s orbit and every point on the second planet’s orbit. Using this, three researchers found that Venus is on average is 1.14 astronomical units (AU) away from Earth and Mercury is 1.04 AU away.

The researchers figured that for any two bodies in the same plane and moving in concentric orbits, the average distance between the two bodies is directly proportional to the radius of the inner orbit.

To validate this corollary, they plotted the planets in their actual elliptical orbits in 3D and ran a simulation for 10,000 years. The simulation recorded the distances between each pair of planets every 24 simulation hours.

The average measured distances deviated from the results from PCM by less than 1% – so their calculation was right. On average, Mercury is Earth’s closest neighbour.

To be completely honest, this isn’t entirely useful information. The researchers’ finding doesn’t change how astronomers and spaceflight planners work. In fact, it could even be a case of ‘data torture’: analysing a large dataset in multiple ways and finding one interesting result – the statistical equivalent of a broken clock being right twice a day.

One astrophysicist told The Wire, “Any physical quantity is interesting to the degree to which it determines the solution of interesting questions. For planetary dynamics, some of the interesting questions are about the evolution of the orbits of the planets, satellites, asteroids, comets and other minor bodies. The physical quantities of interest are the Keplerian orbital elements, whose long-time evolution is in general difficult to calculate.”

In this picture, the “average distance” the researchers have calculated – the astrophysicist said – might not be worthwhile. “Further discussion on this topic may enliven casual conversation but writing more about it could be, in my opinion, a waste of time.”

These are sobering words. However, the researchers’ article does have one very important redeeming quality. Trying to improve stargazing and space-journeying are lofty goals but we often forget that pursuing and celebrating curiosities are valuable, too. So knowing that Mercury is in a certain way closer to Earth is – to name that quality – wow. And wow needn’t be a waste of time.

Pratik Pawar is a science writer and a recipient of the S. Ramaseshan science writing fellowship.

Long Ago, the Number of Meteors Hitting Earth Spiked Suddenly – and Didn’t Stop

Something happened in the Solar System about 300 million years ago, and Earth and the Moon have since been assailed over twice as often by meteors.

About 300 million years ago, something happened. And the Moon was hit by meteorites twice to thrice as often after this period than before.

The Solar System has always been a dangerous place for careless travellers. Out there are large clouds of dust, millions of rocks dislodged from ancient collisions, fragments of comets, meteors and asteroids, even interstellar interlopers. The dangers of space haven’t been limited to radiation and extreme isolation.

But even in this chaotic picture, it is startling to find that the rate at which rocky objects struck the Moon suddenly spiked so sharply. What could’ve happened?

The answer to this question is important because, as a new study notes, if the Moon is being hit faster, then Earth could be as well. We just wouldn’t know it because Earth’s atmosphere burns off many of these objects before they reach the ground. Even when they do, plate tectonics messes with all but traces of the more recent impacts. And then there’s the weather. Our natural satellite has none of these luxuries, and its surface is frequently pocked by small and large rocks.

So the Moon is like “a time capsule for events that happen in our corner of the Solar System,” Sara Mazrouei, a planetary scientist at the University of Toronto and one of the study’s authors, told National Geographic.

However, that doesn’t mean what strikes the Moon stays on the Moon. The lunar surface does undergo some transformations thanks to processes like erosion. Moreover, when larger bodies impact its surface, it shakes and redistributes the looser parts of its soil.

To get around these sources of confusion, the analysts – scientists from the US, the UK and Canada – devised some workarounds.

First, they focused on craters over 10 km in diameter (between the 80º N and 80º S latitudes). The diameter limit was set so high because these impacts are likely to have penetrated the bedrock and chipped off rocks from there to the surface. These rocks are warmer and remain that way for longer than those on the surface.

The researchers also figured that newer craters – formed within the last billion years – would be covered in more such rocks than older ones. This is because the longer the rocks lie around, the likelier they are to be broken up into smaller pieces by micrometeorites, the Moon’s crazy temperature shifts (which recently put paid to an intrepid cotton plant) and other disturbances.

In effect, they were left with a three-way relationship between rock abundance, rock temperature and crater age. And when they brought this to bear on data recorded by the Lunar Reconnaissance Orbiter (LRO), a NASA satellite around the Moon, they made their discovery – described richly by the chart below.

DOI: 10.1126/science.aar4058

DOI: 10.1126/science.aar4058

The x-axis shows the ages of craters in millions of years. The y-axis is self-explanatory, and is a proxy for time. As a first step, look at the dotted line. It’s straight because it assumes that the rate of impacts was constant throughout time. However, the researchers found that the black lines – from LRO data – suggested the real picture wasn’t as straightforward.

Instead, they think the rate of impacts is closer to the blue line, which shows a perceptible shift around 290 million years ago. Its slope beyond this point is gentler than the slope before because the cratering rate has increased, and the fraction changes less quickly as a result.

An even more interesting feature of the chart is the red line, which depicts craters on Earth in the same period. Its flow suggests that the rock barrage that began 290 million years ago is likely going on against Earth as well.

Earth has had a storied relationship with meteors and meteorites. One of the most famous events was when a rock wider than the height of Mt Everest struck Earth 66 million years ago, wiping out all dinosaurs that couldn’t fly and triggering a mass extinction.

If the Moon’s record-keeping has been correct, this cataclysm – and other smaller ones – were part of the ongoing wave of more frequent meteoric events. But to be sure, the scientists had to ascertain that Earth didn’t have fewer impact craters before 300 million years ago because the older craters had been eroded away.

And this they did by studying kimberlite pipes. These are tubular structures about 2 km deep, commonly found embedded within ancient landmasses. They were formed when volcanoes underground exploded in supersonic eruptions millions of years ago, drilling these formations through the crust. They are rich in diamonds and are mined for this purpose.

Kimberlite pipes underwent significant erosion before 650 million years ago, during a period called ‘Snowball Earth’ – but very little after. As a proxy for the amount by which Earth’s surface eroded over time, the pipes suggest there are fewer craters on Earth older than 300 million years simply because the number of craters created since has been increasing at a higher rate.

So there we have it – the beginnings of a new mystery. Something happened in the Solar System about 300 million years ago, and Earth and its Moon have since been assailed over twice as often by meteors. We don’t yet know what this something is, but there are some ideas.

For example, the scientists suspect in their paper that the change “may be due to the breakup of one or more large asteroids in the inner and/or central main asteroid belt”. The tinier of these fragments absorb and reemit sunlight, giving themselves a small kick. As lots of fragments are kicked outward like this, they could become trapped in the gravitational fields of planets and moons, and slowly drift towards them.

Spaceflight institutions like NASA and the Indian Space Research Organisation will find this update useful because they can now recalibrate the threat to their space-based assets. They can also work with military organisations to strengthen their planetary defence systems, if any.

There’s also a second mystery here, so to speak. The scientists were able to identify the shift in impact rates 290 million years ago because they assumed there was only one such shift. It’s possible that a larger dataset, with more than the 111 craters they examined, could throw up even more shifts in the rate from a variety of causes.

This in turn could begin to reveal the full extent of the threats Earth faces, and what we can do to keep from getting wiped out.

NASA Deep Space Probe Reaches Asteroid Deemed Potential Earth Threat

A ‘touch-and-go’ manoeuvre of OSIRIS-REx is planned to snatch organic compounds believed to be on asteroid Bennu.

NASA‘s deep space explorer OSIRIS-REx flew on Monday to within a dozen miles of its destination, a skyscraper-sized asteroid believed to hold organic compounds fundamental to life as well as the potential to collide with Earth in about 150 years.

Launched in September 2016, OSIRIS-REx embarked on NASA‘s unprecedented seven-year mission to conduct a close-up survey of the asteroid Bennu, collect a sample from its surface and return that material to Earth for study.

Bennu, a rocky mass roughly a third of a mile wide and shaped like a giant acorn, orbits the sun at roughly the same distance as Earth and is thought to be rich in carbon-based organic molecules dating back to the earliest days of the solar system. Water, another vital component of the evolution of life, may also be trapped in the asteroid‘s minerals.

Scientists believe that asteroids and comets crashing into early Earth delivered organic compounds and water that seeded the planet for life, and atomic-level analysis of samples from Bennu could help prove that theory.

But there is another, a more existential reason to study Bennu.

Also read: Why NASA Chose Senegal to Find out More About an Asteroid in Outerspace

Scientists estimate there is a one-in-2,700 chance of the asteroid slamming catastrophically into Earth 166 years from now. That probability ranks Bennu No. 2 on NASA‘s catalog of 72 near-Earth objects potentially capable of hitting the planet.

OSIRIS-REx will help scientists understand how heat radiated from the sun is gently steering Bennu on an increasingly menacing course through the solar system. That solar energy is believed to be nudging the asteroid ever closer toward Earth‘s path each time the asteroid makes its closest approach to our planet every six years.

“By the time we collect the sample in 2020 we will have a much better idea of the probability that Bennu would impact Earth in the next 150 years,” mission spokeswoman Erin Morton said.

Scientists have estimated that in 2135 Bennu could pass closer to Earth than the moon, which orbits at a distance of about 250,000 miles, and possibly come closer still sometime between 2175 and 2195.

OSIRIS-REx reached the “preliminary survey” phase of its mission on Monday, soaring to within 12 miles of the asteroid. The spacecraft will pass just 1.2 miles from Bennu in late December, where it will enter the object’s gravitational pull.

From that stage, the spacecraft will begin gradually tightening its orbit around the asteroid, spiraling to within just 6 feet of its surface. OSIRIS-REx will then extend its robot arm to snatch a sample of Bennu’s terrain in a “touch-and-go” manoeuvre set for July 2020.

OSIRIS-REx will later fly back to Earth, jettisoning a capsule bearing the asteroid specimen for a parachute descent in the Utah desert in September 2023.

NASA is developing a strategy for deflecting Bennu, or any other asteroid found to be on a collision course with Earth, by use of a special spacecraft to slam into the object hard enough to nudge it onto a safer path, said Lindley Johnson, a planetary defence officer with NASA‘s Science Mission Directorate.

“But this is all dependent on the outcome of a very close approach that Bennu has with Earth in September 2135,” Johnson said. “We’ll just need to wait and see. Rather, our great-great-grandchildren will need to see.”

(Reuters)

The Story of Dust, Through Space and Time

Unlike our search thus far for extraterrestrial companionship, we are not alone in feeling beset by dust.

What is dust?

It feels ridiculous just asking that question sitting in India. Dust is everywhere. On the roads, in your nose, in your lungs. You lock up your house, go on a month-long holiday and come back, and there’s a fine patina on the table. It’s inside your laptop, driving the cooling fan nuts.

It is also in the atmosphere, in orbit around Earth, in outer space even. It makes up nightmarish storms on Mars. Philip Pullman and Steven Erikson have written books fantasising about it. Dust is omnipresent. (The only dustless places I’ve seen are in stock photos strewn across the internet.)

But what exactly is it, and where did it all come from?

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Earth

The Saharan dust plume in June 2018. Credit: NASA/Earth Observatory

The Saharan dust plume in June 2018. Credit: NASA/Earth Observatory

Dust is fine particulate matter. It originates from a tremendous variety of sources. The atmospheric – or aeolian – dust we are so familiar with is composed of small particles sheared off of solid objects. For example, fast-blowing winds carry particles away from loose, dry soil into the air, giving rise to what is called fugitive dust. Another source is the smoke from exhaust pipes.

Yet another is mites of the family Pyroglyphidae. They eat flakes of skin, including those shed by humans, and digest them with enzymes that stay on in their poop. In your house, exposure to their poop (considered a form of dust) can trigger asthma attacks.

Winds lift particulate matter off Earth’s surface and transport them into the troposphere. Once dust gets up there, it acts like an aerosol, trapping heat below it and causing Earth’s surface to warm. Once it collects in sufficient quantities, it begins to affect the weather of regions below it, including rainfall patterns.

Dust particles smaller than 10 microns get into your lungs and affect your respiratory health. They conspire with other pollutants and, taking advantage of slow-moving winds, stagnate over India’s National Capital Region during winter. Particles smaller than 2.5 microns “increase age-specific mortality risk” (source) and send hospital admissions soaring.

There is also dust that travels thousands of kilometres to affect far-flung parts of the world. The “Sahara is the world’s largest source of desert dust”, according to one study. In June this year, the Atlantic Ocean’s tropical area experienced its dustiest period in 15 years when a huge billow blew over from northeast Chad towards the mid-Americas. According to NASA’s Earth Observatory, Saharan dust “helps build beaches in the Caribbean and fertilises soils in the Amazon.”

But speaking of dust that migrates large distances, the transatlantic plume seems much less of a journey than the dust brought to Earth by meteorites that have travelled hundreds of thousands of kilometres through space. As these rocks streak towards the ground, the atmosphere burns off dust-like matter from their surfaces, leaving them hanging in the upper atmosphere.

Atoms released by these particles into the mesosphere drift into the planet’s circulation system, moving from pole to pole over many months. They interact with other particles to leave behind a trail of charged particles. Scientists then use radar to track these particles to learn more about the circulation itself. Some dust particles of extraterrestrial origin also reach Earth’s surface in time. They could carry imprints of physical and chemical reactions they might have experienced in outer space, even from billions of years ago.

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Orbit

Dust in the Andromeda Galaxy, as seen by the Spitzer Space Telescope. Credit: NASA/JPL-Caltech/K. Gordon (University of Arizona)

Dust in the Andromeda Galaxy, as seen by the Spitzer Space Telescope. Credit: NASA/JPL-Caltech/K. Gordon (University of Arizona)

In the mid-20th century, researchers used optical data and mathematical arguments to figure that about four million tonnes of meteoric dust entered our planet’s atmosphere every year. This was cause for alarm: the figure suggested that the number of meteorites in space was much higher than thought. In turn, the threat to our satellites could have been underestimated. More careful assessments later brought the figure down. A 2013 review states that 10-40 tonnes of meteoric dust slams into Earth’s atmosphere every day.

Still, this figure isn’t low – and its effects are exacerbated by the debris humans themselves are putting in orbit around Earth. The Wikipedia article on ‘space debris’ carefully notes, “As of … July 2016, the United States Strategic Command tracked a total of 17,852 artificial objects in orbit above the Earth, including 1,419 operational satellites.” But only one line later, the number of objects smaller than 1 cm explodes to 170 million.

If a mote of dust weighing 0.00001 kg carried by a 1.4 m/s breeze strikes your face, you are not going to feel anything. This is because its momentum – the product of its mass and velocity – is very low. But when a particle weighing one-hundredth of a gram strikes a satellite at a relative velocity of 1.5 km/s, its momentum jumps a thousandfold. Suddenly, it is able to damage critical components and sensitively engineered surfaces, ending million-dollar, multi-year missions in seconds. One study suggests such particles, if travelling fast enough, can also generate tiny shockwaves.

Before our next stop on the Dust Voyage, let’s take a small break in sci-fi. The mid-century overestimation of meteoric dust flux may have prompted Arthur C. Clarke to write his 1961 novel, A Fall of Moondust. In the story, a cruise-liner called the Selene takes tourists over a basin of superfine dust apparently of meteoric origin. But one day, a natural disaster causes the Selene to sink into the dust, trapping its passengers in life-threatening conditions. After much despair, a rescue mission is mounted when an astronomer spots a heat-trail pointing to the Selene’s location from space, from onboard a spacecraft called Lagrange II.

This name is a reference to the famous Lagrange points. As Earth orbits the Sun, and the Moon orbits Earth, their combined gravitational fields give rise to five points in space where the force acting on an object is just right for it to maintain its position relative to Earth and the Sun. These are called L1, L2, L3, L4 and L5.

A contour plot of the effective potential of the Earth-Sun system, showing the five Lagrange points. Credit: NASA and Xander89, CC BY 3.0

A contour plot of the effective potential of the Earth-Sun system, showing the five Lagrange points. Credit: NASA and Xander89, CC BY 3.0

The Indian Space Research Organisation (ISRO) plans to launch its Aditya satellite, to study the Sun, to L1. This is useful because at L1, Aditya’s view of the Sun won’t be blocked by Earth. However, objects at L1, L2 and L3 have an unstable equilibrium. Without some station-keeping measures now and then, they tend to fall out of their positions.

But this isn’t so with L4 and L5, objects at which remain in a more stable equilibrium. And like anything that’s been lying around for a while, they collect dust.

In the 1950s, the Polish astronomer Kazimierz Kordylewski claimed to have spotted two clouds of dust at L4 and L5. These nebulous collections of particulate matter have since been called Kordylewski clouds. Other astronomers have contested their existence, however. For example, the Hiten satellite could not find any notable dust concentrations in the L4 and L5 regions in 2009. Some argued that Hiten could have missed them because the dust clouds are too spread out.

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Space

An artist's impression of dust formation during a supernova explosion. Caption and credit: ESO/M. Kornmesser, CC BY 4.0

An artist’s impression of dust formation during a supernova explosion. Caption and credit: ESO/M. Kornmesser, CC BY 4.0

Only two weeks ago, Hungarian astronomers claimed to have confirmed the presence of dust clouds in these regions (their papers here and here). Because the L4 and L5 regions are of interest for future space missions, astronomers will now have to validate this finding and – if they do – assess the density of dust and the attendant probabilities of threat.

Unlike Kordylewski, who took photographs from a mountaintop, the Hungarian group banked on dust’s ability to polarise light. Light is electromagnetic radiation. Each wave of light consists of an electric and a magnetic field oscillating perpendicular to each other. Imagine various waves of light approaching dust, their electric fields pointed in arbitrary directions. After they strike the dust, however, the particles polarise the waves, causing all of the electric fields to line up with one particular orientation.

When astronomers detect such light, they know that it has encountered dust in its path. Using different instruments and analytical techniques, they can then map the distribution of dust in space through which the light has passed.

This is how, for example, the European Space Agency’s Planck telescope was able to draw up a view of dust around the Milky Way.

A map of dust in and around the Milky Way galaxy, as observed by the ESA Planck telescope. Credit: NASA

A map of dust in and around the Milky Way galaxy, as observed by the ESA Planck telescope. Credit: NASA

That’s billions upon billions of tonnes. Don’t your complaints about dust around the house pale in comparison?

And even at this scale, it has been a nuisance. We don’t know if the galaxy is complaining but Brian Keating certainly did.

In March 2014, Keating and his team, with the Harvard-Smithsonian Centre for Astrophysics, announced that they had found signs that the universe’s volume had increased by a factor of 1080 in just 10-33 seconds a moment after its birth in the Big Bang. About 380,000 years later, radiation leftover from the Big Bang – called the cosmic microwave background (CMB) – came into being. Keating and co. were using the BICEP2 detector at the South Pole to find imprints of cosmic inflation on the CMB. The smoking gun: light of a certain wavelength polarised by gravitational waves from the early universe.

While the announcement was made with great fanfare – as the “discovery of the decade” and whatnot – their claim quickly became suspect. Data from the Planck telescope and other observatories soon showed that what Keating’s team had found was in fact light polarised by galactic dust. Just like that, their ambition of winning a Nobel Prize came crashing down. Ash to ash, dust to dust.

You probably ask, “Hasn’t it done enough? Can we stop now?” No. We must persevere, for dust has done even more, and we have come so close. For example, look at the Milky Way dust-map. Where could all that dust have come from?

This is where the story of dust takes a more favourable turn. We have all heard it said that we are made of stardust. While it would be futile to try and track where the dust of ourselves came from, understanding dust itself requires us to look to the stars.

The storms on Earth or Mars that stir dust up into the air are feeble breaths against the colossal turbulence of stellar ruination. Stars can die in one of many ways depending on their size. The supernovae are the most spectacular. In a standard Type 1a supernova, an entire white dwarf star undergoes nuclear fusion, completely disintegrating and throwing matter out at over 5,000 km/s. More massive stars undergo core collapse, expelling their outermost layers into space in a death-sneeze before what is left implodes into a neutron star or a black hole.

Any which way, the material released into space forms giant clouds that disperse slowly over millions of years. If they are in the presence of a black hole, then they are trapped in an accretion disk around it, accelerated, heated and energised by radiation and magnetic fields. The luckier motes may float away to encounter other stars, planets or other objects, or even collide with other dust and gas clouds. Such interactions are very difficult to model – but there is no doubt that these they are all essentially driven by the four fundamental forces of nature.

One of them is the force of gravity. When a gas/dust cloud becomes so large that its collective gravitational pull keeps it from dispersing, it could collapse to form another star, and live to see another epoch.

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Together

The Cat's Paw Nebula, imaged here by NASA's Spitzer Space Telescope, lies inside the Milky Way Galaxy and is located in the constellation Scorpius. Its distance from Earth is estimated to be between 4,200 light years and 5,500 light years. The green areas show regions where radiation from hot stars collided with large molecules and small dust grains called polycyclic aromatic hydrocarbons, causing them to fluoresce. Caption and credit: NASA/JPL-Caltech, Wikimedia Commons

The Cat’s Paw Nebula, imaged here by NASA’s Spitzer Space Telescope, lies between 4,200 lightyears and 5,500 lightyears from Earth. The green areas show regions where radiation from hot stars collided with large molecules and small dust grains called polycyclic aromatic hydrocarbons, causing them to fluoresce. Caption and credit: NASA/JPL-Caltech, Wikimedia Commons

This way, stars are cosmic engines. They keep matter – including dust – in motion. They may not be the only ones to do so but given the presence of stars throughout the (observable) universe, they certainly play a major part. When they are not coming to life or going out of it, their gravitational pull influences the trajectories of other, smaller bodies around them, including comets, asteroids and other spacefaring rocks.

The Solar System itself is considered to have been condensed out of a large disk of dirt and dust made of various elements surrounding a young Sun – a disk of leftovers from the star’s birth. Different planets formed based on the availability of different volumes of different materials at different times. Jupiter is believed to have come first, and the inner planets, including Earth, to have come last.

But no matter; life here had whatever it needed to take root. Scientists are still figuring what those ingredients could have been and their provenance. One theory is that they included compounds of carbon and hydrogen called polycyclic aromatic hydrocarbons, and that they first formed – you guessed it – among the dust meandering through space.

They could then have been ferried to Earth by meteors and comets, perhaps swung towards Earth’s orbit by the Sun’s gravity. When a comet gets closer to a star, for instance, material on its surface begins to evaporate, forming a streaky tail of gas and dust. When Earth passes through a region where the tail’s remnants and other small, rocky debris have lingered, they enter the atmosphere as a meteor shower.

Dust really is everywhere, and it seldom gets the credit it is due. It has been and continues to be a pesky part of daily life. However, unlike our search thus far for extraterrestrial companionship, we are not alone in feeling beset by dust.

Start Mining Asteroids for Faster Data and a Cleaner Planet

An asteroid-mining infrastructure could help to solve a major impending resource problem.

An asteroid-mining infrastructure could help to solve a major impending resource problem.

Artist’s impression of asteroid mining. Credit: NASA

Mining asteroids might seem like the stuff of science fiction, but there are companies and a few governments already working hard to make it real. This should not be surprising: compared with the breathtaking bridges that engineers build on Earth, asteroid-mining is a simple, small-scale operation requiring only modest technological advances. If anything is lacking, it is the imagination to see how plausible it has become. I am afraid only that it might not arrive soon enough to address the urgent resource challenges that the world is facing right now.

As an academic researcher, I work with several asteroid–mining companies to address that urgency. I depend on their funding, so there are trade secrets I cannot share. However, I can reveal the core reasons why I am optimistic about the business case for asteroid-mining, and what it will mean for our future.

Many people are skeptical of asteroid-mining because they imagine that the goal is to bring platinum back for sale in Earth’s metals market. Reporters repeatedly cite an irresistible statistic that the platinum in an asteroid can be worth trillions of US dollars, but anyone with an understanding of economics realises that bringing home a huge stash of precious metal would crash the market, reducing the valuation of the asteroid.

On the other hand, if the plan is to dole out platinum in small quantities to keep the valuation high (as it is done in the diamond industry), then how could asteroid companies compete with terrestrial mining companies that benefit from a mature, low-cost terrestrial supply chain and transportation network?

This is exactly why platinum is not the objective of asteroid-mining. Instead, the first product from asteroids will be something much less obviously precious: water.

To rocket scientists, water is the raw material for propellant. Launching water from Earth into space consumes a lot of propellant, which makes the whole concept self-defeating. Fortunately, water is abundant in space, where it is much easier to move around. Water can be readily extracted from clay minerals in a common class of small bodies known as carbonaceous asteroids. Once separated from the minerals, the water can then be split by electricity (a process called electrolysis) into hydrogen and oxygen to make rocket propellant – the key ingredients of rocket fuel.

Using rocket propellant produced in space will reduce the cost of doing everything else in space, initiating a virtuous cycle for the off-Earth supply chain and transportation network. Before that can happen, though, we must find the customers who can get the whole process started.

Who will buy rocket fuel made from asteroid water? One concept is to sell it to telecommunications companies for boosting satellites into orbit. A decade ago, most satellites were launched with a small upper-stage rocket attached. The rocket initially lofts the satellite into geostationary transfer orbit, a highly elliptical orbit having perigee (the low point) just a few hundred kilometres above the Earth’s surface, and apogee (the high point) about 36,000 kilometres higher. The spacecraft coasts to apogee, where the rocket fires and circularises the orbit so that the satellite can begin selling data to customers. The cost of the disposable upper-stage rocket is very high, however.

Today, most satellite owners place a lightweight electric thruster on the spacecraft instead. Such thrusters are cheaper and more efficient, but very weak. It takes six to 12 months for satellites to reach final orbit. Time is money, so this delay still costs the satellite-owners hundreds of millions of dollars in lost revenues.

Asteroid-mining will provide a third option. A mining company will sell water to an in-space transportation company, which will use it to refuel a space tug parked in Earth orbit. The tug will dock with the newly launched satellite in geostationary transfer orbit, and boost it to the final orbit quickly, within a day.

According to our calculations, the total cost for this service, including capital recovery, finance charges, insurance and profit for all parties, will be less than the lost revenues of the current method, so that means there is a business case. The only concern is whether there are enough early customers to get the service established.

Here is where the national space agencies like NASA can help. If they develop an in-space refuelling depot to lower their costs for exploring the Moon or Mars, and if they give out commercial contracts for some of this space water, they will lower the capital investment and risk for the new mining companies. In this way, government agencies can ensure the earlier success of private space industry. This is a legitimate role for government because taxpayers will greatly benefit.

An asteroid-mining infrastructure could help to solve a major impending resource problem. Within a decade or two, the current system of satellites and fiber optics will not be able to keep up with the demand for wireless and internet data. I know of no solution apart from building antennas in space that are too large to launch on rockets, because nothing else scales up quickly enough to meet the data needs that will grow exponentially through to the end of the century. Metal from asteroids will not be sold on Earth, where it would be too expensive. It will remain in space, transmitting precious data down into the digital market.

Similar arguments can be made that generating solar energy in space will, by sometime this century, be cheaper than generating energy on Earth through any known method. The energy might then be beamed to the ground via microwaves. Moving most of the energy sector into space will unburden the planet of the environmental impacts of energy generation, along with the entire supply chain that supports it. Even wind and solar disrupt large areas of land.

Off-planet energy generation could eliminate one-quarter of the human industrial footprint by 2100, by some estimates. This does not even take into account the exponentially growing energy footprint of computer manufacturing and operation, which is terrifying from an environmental perspective.

Note that none of these ideas involves bringing asteroid materials back for sale on Earth. The real value of space-based mining will be to create a space-based industry that benefits all of us. The primary import from space will be massless photons carrying data and energy.

The important point our government leaders should understand is that investing in space-mining is a safe bet on our future, one of the safest they can make. NASA and the other space agencies will get more science and exploration, plus greater geopolitical presence, for less cost than their current way of doing business. Saving the Earth and improving our quality of life might simply be side effects we get for free.Aeon counter – do not remove

This article was originally published at Aeon and has been republished under Creative Commons.

Cassini Readies for 31 Km/s Dive Into Saturn, Bringing Epic Mission to Close

While Cassini is celebrated in the popular literature for its stunning photographs of Saturn’s rings more often, its more unique contributions have advanced our understanding of the planet’s moons.

While Cassini is often celebrated in the popular literature for its stunning photographs of Saturn’s rings, its more unique contributions have advanced our understanding of the planet’s moons.

An artist's illustration of Cassini zooming in towards Saturn. Credit: NASA/JPL-Caltech

An artist’s illustration of Cassini zooming in towards Saturn. Credit: NASA/JPL-Caltech

After 13 years orbiting Saturn, its majestic rings and plethora of moons, the Cassini space probe will make a headlong dive into the gas giant and burn up on September 15. NASA has dubbed the event the ‘Grand Finale’.

The probe’s instruments will be awake during its final mission, transmitting data about Saturn’s atmosphere to scientists on Earth, until they’re fried to a crisp by the heat and pressure.

For over a decade, the Cassini probe has been humankind’s foremost eye in the outer Solar System. It has studied the planet, its rings and its 62 moons in fine detail. Almost everything we know about them is because of the probe, and we know a crazy lot now than we did before Cassini.

Cassini was named for the Italian astronomer Giovanni Domenico Cassini, who discovered four of Saturn’s moons in the mid- to late-17th century. It was a joint operation between NASA, the European Space Agency and the Italian Space Agency in 1997, and cost $2.1 billion to build and launch. It reached Saturn after seven years. It was expected to complete its primary mission by 2008 (it did), at which point it received an extension for two years, followed by a second one in 2010. In all this time, Cassini has travelled almost 2 billion km in orbits around Saturn and beamed back over 453,000 images.

‘Ocean worlds’

This graphic summarizes Cassini's 13 years orbiting Saturn, with moon flybys grouped into rows. The Grand Finale orbits are highlighted in their own row at the end. Caption & credit: NASA/JPL-Caltech

This graphic summarises Cassini’s 13 years orbiting Saturn, with moon flybys grouped into rows. The Grand Finale orbits are highlighted in their own row at the end. Click to enlarge. Caption & credit: NASA/JPL-Caltech

On December 25, 2004, a lander on-board the probe, called Huygens, was deployed to the surface of Titan, Saturn’s largest moon (bigger than Mercury) and one of only two bodies in the Solar System known to have liquids on its surface.

Through Huygens and Cassini data, scientists today know that Titan has a complex chemical ecosystem made up of hydrocarbons. In fact, while Cassini is celebrated in the popular literature for its stunning photographs of Saturn’s rings more often, one of its most unique contributions has been to advance our understanding of the moons of the outer Solar System.

Astronomers study what moons and asteroids are made of to understand where they could’ve come from because many of them are likely to be leftovers of the ingredients that formed the planets. For example, the asteroids beyond the orbit of Pluto have a certain composition while those between the orbits of Mars and Jupiter have a mixed composition. So this indicates some of the outer asteroids were pulled in by a giant planet into the inner asteroid belt some time in the past.

Thanks to Cassini, we’ve a more thorough idea of what Saturn’s moons are like, how they might’ve got there and how their properties affect the Saturnian system as a whole. The more notable of these moons, apart from Titan, are Enceladus, Rhea, Hyperion, Iapetus, Dione and Phoebe. Additionally, Cassini also helped discover seven new moons (Methone, Pallene, Polydeuces, Daphnis, Anthe, Aegaeon and one known only as S/2009 S 1).

On Titan, Cassini found that there are lakes, rivers and seas of liquid methane and ethane, methane clouds wafting through its skies and raining down seasonally. Titan’s lakes have tiny waves and fizz with nitrogen bubbles. Its deserts have electric sand that sticks together to form giant dunes. Using Cassini and Huygens data, scientists have been able to identify the presence of individual molecules and speculate that some of them could lend themselves to strange forms of life. To explore this world further, NASA has been mulling missions on and off.

As for Enceladus: Cassini found that it is a giant ball of ice containing a global ocean of salty liquid water a few kilometres underground. Perhaps the first alien life we find will be much closer home – and we wouldn’t be thinking this if not for Cassini. In fact, more generally, this discovery turned astronomers’ attention to a class of planetary bodies called ‘ocean worlds’, which they’re exploring to this day. As Thomas Zurbuchen, associate administrator for NASA’s science mission directorate, Washington, said in a statement, “Cassini has transformed our thinking in so many ways, but especially with regard to surprising places in the solar system where life could potentially gain a foothold.”

Also read: NASA finds more signs Saturn’s icy moon can support life

Cassini also found that Rhea has a charged surface that radiolyses its surface ice, creating a thin atmosphere of oxygen, ozone and hydrogen peroxide. That Hyperion’s density is so low that 40% of it is empty. That Iapetus has an inexplicable ridge on its equator running around most of the moon. That Dione – like Enceladus – could be harbouring a water ocean underground. That Phoebe could originally have been an asteroid in the outer belt captured by Saturn.

And on Saturn itself, Cassini studied the planet’s rings, what they were made of, how they were distributed in space and how they were being replenished. It studied a giant hurricane on the planet’s south pole in 2006 and, five years later, tracked the aftereffects of the largest storm ever observed in the Solar System in Saturn’s stratosphere. Cassini also observed Saturn’s north pole, which is ringed by a storm in the shape of an unmoving hexagon wider than Earth. It explored an atmosphere that is less dense than water vapour. In all, Cassini revealed “a giant world ruled by raging storms and delicate harmonies of gravity”.

As it happens, one of these “harmonies” may have affected life on Earth. According to Alex Parker, a planetary astronomer at the Southwest Research Institute, Texas, the meteor that wiped out the dinosaurs 65 million years ago could have been a rock drifting aimlessly through space before it got too close to Saturn, whose gravity could then have flung it towards Earth. In Parker’s words: “there is a non-negligible chance that Saturn killed the dinosaurs.”

Anyway, Cassini has also provided a clearer view of which questions future probes to the planet need to be able to answer. As the authors of a 2009 book asked,

What is the bulk composition of the planet? Does it have a helium core? Is it enriched in noble gases like Jupiter? What powers and controls its gigantic storms? We have learned that we can measure an outer magnetic field that is filtered from its non-axisymmetric components, but what is Saturn’s inner magnetic field? What are the rings made of and when were they formed? Was the proto-solar disk progressively photo-evaporated of its hydrogen and helium while forming its planets? … Did Jupiter and Saturn form at the same time from cores of similar masses? … Finally, the theory behind the existence of its rings is still to be confirmed

Also read: No majestic lord of the rings, Saturn is really a master of deception

Sadness and joy

Evidently, Cassini has had a journey grander than its finale, and recounting all of its findings would take many hundreds of pages. It surveyed a remote neighbourhood of the Solar System all alone for over a decade and forged a strong relationship with scientists interested in what it was finding. Scientists have also imagined Cassini as having forged a relationship with Saturn in turn, and are loathe to speak about the mission’s end as suicide. Instead, many have cast it as the eternal union of two close friends.

Moreover, today, there are two more probes in the general area: Juno is studying Jupiter while New Horizons, after flying by Pluto in 2016, is now headed to study the outer asteroid belt. Based on Cassini’s findings, NASA has planned another mission – tentatively called the Clipper – to Jupiter’s moon Europa in the 2020s.

It’s for these reasons that the end of Cassini’s mission on September 15 has evoked sadness in the astronomy community. “The public mourning of Cassini serves as another example of the complicated relationship between humans and machines, and of the tendency of humans to anthropomorphise robots and care about them,” Marina Koren wrote in The Atlantic. “Even the slightest perceived hints of life in a machine – like Cassini ‘fighting to keep its antenna pointed at Earth’ – can cause people to see it as something other than just a collection of sensors and circuitry, and then react to it in an emotional way.”

Cassini’s ‘Grand Finale’ was brought on by Cassini itself, so to speak. Because Titan and Enceladus could be home to life, leaving the probe drifting in space near them risks contaminating the moons with its parts. One of those parts is 32.2 kg of plutonium-238, the heat of whose radioactive decay powers three radioisotope thermoelectric generators on Cassini.

Also read: The radioisotope generator pulsing in ISRO’s future

Instead, NASA has decided to send Cassini blazing down into Saturn. (If you prefer an alternative explanation, Parker – of the ‘Saturn killed the dinosaurs’ claim – has one: “symbolic act of cosmic justice for the former residents of planet Earth”.) The sequence of events was set in motion on April 26 this year, when the probe began to orbit Saturn such that it passed between the planet and its rings. There were 22 such ‘Grand Finale’ dives in the all, and the last one will plunge Cassini into darkness.

Cassini's last 22 orbits. Credit: NASA/JPL-Caltech

Cassini’s last 22 orbits. Credit: NASA/JPL-Caltech

While its cameras will have been shut off a day in advance, the probe’s remaining eight instruments will keep recording and transmitting data about Saturn’s atmosphere on their way down, providing humankind an invaluable peek into an inhospitable world.

Until, shortly after 5:25 pm IST, the signal goes quiet.

Remembering M.K. Vainu Bappu, the Indian Comet Hunter

Apart from helming the International Astronomical Union, Bappu is also the only Indian so far to have a comet and an asteroid named after him.

Apart from helming the International Astronomical Union, Bappu is also the only Indian so far to have a comet and an asteroid named after him.

The Vainu Bappu Observatory in Kavalur, Tamil Nadu. Credit: Prateek Karandikar/Wikimedia Commons, CC BY-SA 4.0

The Vainu Bappu Observatory in Kavalur, Tamil Nadu. Credit: Prateek Karandikar/Wikimedia Commons, CC BY-SA 4.0

Aswin Sekhar is an Indian astrophysicist who works at the Centre for Earth Evolution and Dynamics, Faculty of Mathematics and Natural Sciences, University of Oslo.

When an astronomer becomes the first to discover a comet, and has the celestial object named for her, it is bound to be a special moment in her life. Typically scientists and governments alike applaud such achievements and wear them with pride.

But for Manali Kallat Vainu Bappu, the exact opposite happened. When he co-discovered a comet in 1949, Indian diplomats from the country’s embassy in Washington DC sent him a ‘severe warning’ instructing him to concentrate on his PhD rather than ‘waste’ time looking for comets on a government scholarship (his was being funded by the erstwhile Government of Hyderabad). This was perhaps the sole day in history when a professional astronomer was reprimanded for making an important discovery.

However, the International Astronomical Union (IAU) was gracious on this matter. It sidestepped all the bureaucratic controversies, followed its norms and officially named the comet C/1949 N1 as the Bappu-Bok-Newkirk comet. For this, Bappu was awarded the Donhoe Comet Medal by the Astronomical Society of the Pacific the same year.

Meanwhile, because the letter from the Indian officials was beginning to threaten his scholarship, a distinguished cometary scientist named Fred Lawrence Whipple sent a detailed reply. He wrote, “This is the first occasion in my experience in which a foreign government has taken on itself criticising our educational methods in the Astronomy department of Harvard University.” Whipple added that it would have been better for the Indian government to have written directly to the authorities at Harvard University, where Bappu was studying, rather than reprimand the student in a way that jeopardised his education.

It was no small thing to have Whipple on your side: he advanced one of the most popular theories of the origins and evolution of comets. His defence of Bappu served the latter very well. Moreover, Bappu himself was at Harvard thanks to the efforts of the astrophysicist Harlow Shapley, known for estimating the size of the Milky Way. In the course of his PhD and after, Bappu would go on to discover the important Wilson-Bappu effect. It described a direct correlation between a star’s brightness and electromagnetic radiation emanating from a part of its surface, and used to this day to determine certain properties of stars.

Bappu was instrumental as an institution-builder in India. He headed the historically rich Kodaikanal Solar Observatory after he returned from the US, some time between 1957 and 1960. The reputed Indian Institute of Astrophysics (IIAP) based at Bangalore was his brainchild, set up in 1971. After Shapley’s famous lament in 1947 that India had produced many famous astronomers but had almost no astronomical facilities, it became Bappu’s grand vision to set up a network of observatories in different parts of the country – a vision that was adopted by many astronomers and administrators in his time and after. Before he setting up the IIAP, he had installed the Manora Park observatory in Nainital and, soon after, from 1960, worked at the Kodaikanal Observatory, then the country’s largest.

Thanks to his initiatives, India boasted of a dozen world-class facilities to observe the skies in many wavelengths by 2000. In recognition of his work, he was elected president of the IAU in 1979. He remains the only Indian to have held this position. However, while on his way to Greece to address the 18th IAU General Assembly in 1982 as its new president, he suffered a medical crisis in Munich and breathed his last. The IAU, during its 19th General Assembly held in New Delhi (bringing the IAU-GA to India had been Bappu’s dream), honoured its former president by naming an asteroid after him: 2596 Vainu Bappu.

His early death (at 55 years) also meant he couldn’t live long enough to see the Kavalur telescope project completed. The Vainu Bappu Observatory (VBO) and the Vainu Bappu Telescope (VBT) – both at Kavalur – came to be named for him four years later, in 1986. VBT is India’s biggest operational optical telescope and has various accomplishments to its credit – including the discovery of an atmosphere around Jupiter’s moon Ganymede in 1972 and the confirmation that Uranus possessed rings in 1977. It also reaffirmed the presence of a thin outer ring around Saturn in 1984 and helped discover asteroid 4130 in 1988. The latter came to be named for Srinivasa Ramanujan. VBO and VBT continue to play important roles in the evolution of Indian astrophysics.

Klim Churyumov (sitting). Credit: Trond Erik Hillestad

Klim Churyumov (sitting). Credit: Trond Erik Hillestad

During a conference organised by the IAU and held in the Netherlands last year, I met Klim Churyumov, famous for co-discovering the comet that the European Space Agency’s Rosetta mission visited in 2015. Churyumov took an affectionate jibe at me, asking if he’d be punished in India for his famous finding, hinting at the Bappu incident almost seven decades ago. I reassured him that the times had changed and that he ought to visit the VBO. Sadly, he died before he could take me up on the offer.

Apart from helming the IAU, Bappu is also the only Indian so far to have a comet and an asteroid named after him. His life has some parallels in that of Edmond Halley, the English physicist who predicted the orbit of the comet named after him but didn’t live long enough to witness its return and prove him definitively right. Similarly, had Bappu lived for only a few years more, he would have been able to use the VBT at Kavalur and once again see the comet that got him into trouble all those years ago.

The Two NASA Missions That Will Study Rocky Fossils of a Younger Solar System

Lucy and Psyche are a part of NASA’s Discovery Program, whose raison d’être is to explore our planetary neighbourhood using “faster, better, cheaper” missions.

Lucy and Psyche are a part of NASA’s Discovery Program, whose raison d’être is to explore our planetary neighbourhood using “faster, better, cheaper” missions.

Lucy flying by Eurybates and Psyche, by 16 Psyche, in this artist's conceptualisation. Credit: SwRI and SSL/Peter Rubin

Lucy flying by Eurybates and Psyche, by 16 Psyche, in this artist’s conceptualisation. Credit: SwRI and SSL/Peter Rubin

In January 2017, NASA selected two low-cost, highly specialised missions to explore very strange asteroids in our Solar System.

The selected missions are named Lucy and Psyche as a part of its Discovery Program, whose raison d’être is to explore our planetary neighbourhood using “faster, better, cheaper” missions. The main asteroid belt – between the orbits of Mars and Jupiter – holds a lot of mysteries astronomers are keen to resolve. It is especially instrumental in understanding how planets form because the asteroids are primitive bodies that could have formed a planet had Jupiter not existed.

The Psyche mission will check out an asteroid in the main belt called 16 Psyche. This rock is one of the ten most massive in the belt. It is metallic in nature, leading scientists to believe that it could be the core of a once-Mars sized planet that has since broken up. The most likely scenario that could have caused this is thought to be a violent collision that vaporised the crust but left the core almost intact. Psyche will help understand planetary formation, especially the processes that contribute to the formation of the core, mantle and crust.

The Lucy mission will travel even further out – to Jupiter to examine six Trojan asteroids. Trojans are bodies that are present in Lagrange points. These are places around a planet’s orbit where the opposing gravitational attraction from the planet and the Sun subtract such that the remaining force can be balanced out by the centrifugal force experienced by a smaller body at that point. So when natural bodies (like asteroids) and artificial objects (like space telescopes) wind up at a Lagrange point, they’re aren’t forced away from that position because the centrifugal force they experience squares off against the Sun-planet forces. As a result, they become space-based parking lots. Each body has five Lagrange points.

A contour plot showing the positions of the five Lagrange points. The contours depict the intensity of the gravitational field surrounding the planet and the Sun. Credit: NASA/Wikimedia Commons, CC BY 3.0

A contour plot showing the positions of the five Lagrange points. The contours depict the intensity of the gravitational field surrounding the planet and the Sun. Credit: NASA/Wikimedia Commons, CC BY 3.0

Jupiter’s trojans are asteroids that share its orbit around the Sun at the L4 and L5 points. Some orbit ahead of Jupiter while some, behind. Nearly all planets have trojans at one or both of these points. Earth and Venus have one trojan each – called 2010 TK7 and 2013 ND15, respectively – while others have more. These trojans co-orbit 60º ahead and behind a planet.

Lucy will first visit the trojans that orbit ahead of Jupiter and fly by four of them: Eurybates, Polymele, Leucus and Orus. The craft will then return to Earth to get a gravity assist by swinging around the planet, and then visit two more trojans trailing Jupiter (Patroclus and Menoetius).

This complex manoeuvre is necessary because the two groups of Trojans are on either side of Jupiter. It would be a long and arduous fuel-intensive task to move the craft from one group to the other, either bypassing the terrible gravitational pull of Jupiter or going all the way around the Sun in a nearly 12-year orbit journey. Flying directly back to Earth, making a U-turn and then visiting Jupiter’s other side offers Lucy not only a short route but also the necessary gravitational kick to speed up on its way back.

Lucy's journey. Credit: NASA

Lucy’s journey. Credit: NASA

The Lucy mission is named after the famous Lucy Australopithecus skeleton that was discovered in 1974. The remains of this female individual belonged to the Hominini species, derived from the same common ancestor as our Homo sapiens and the chimpanzees. Lucy herself was named after the Beatles song Lucy in the Sky With Diamonds, which was playing all day in the expedition camp when the remains were unearthed. The Lucy mission was so named because the trojans are ‘fossils’ of planetary formation and could provide clues into the structure of the early Solar system. Lucy will fly past asteroid 52246 Donaldjohanson, named for the fossil’s discoverer.

Psyche is named after its destination, the asteroid 16 Psyche. It was discovered in 1852 – among the first of its kind to be. It was named after the Greek mythological character Psyche, whose name means ‘soul’.

“This is an opportunity to explore a new type of world – not one of rock or ice but of metal,” said Psyche’s principal investigator Lindy Elkins-Tanton, of the Arizona State University in Tempe, in a statement. “16 Psyche is the only known object of its kind in the solar system, and this is the only way humans will ever visit a core. We learn about inner space by visiting outer space.”

The two missions are the thirteenth and fourteenth Discovery missions to be selected. As the asteroid belt is so far away from us, it will take both missions over five years to reach their destinations. Lucy will launch in 2021 and reach the trojans in 2027. Psyche will launch in 2023 and reach 16 Psyche in 2030. Previous Discovery Program missions have included the Pathfinder (on Mars), Dawn (which visited Vesta and is now in orbit around Ceres) and the Kepler observatory (which has identified over 3,000 exoplanets so far).

Sandhya Ramesh is a science writer focusing on astronomy and earth science.

Asteroid-Bound OSIRIS-REx Set to Begin New Quest for Life’s Origins

The ambitious seven-year mission will visit the asteroid Bennu and bring back samples scientists think might contain the building blocks of life.

The ambitious seven-year mission will visit the asteroid Bennu and bring back samples scientists think might contain the building blocks of Earthlife.

This artist's concept shows the Origins Spectral Interpretation Resource Identification Security - Regolith Explorer (OSIRIS-REx) spacecraft contacting the asteroid Bennu with the Touch-And-Go Sample Arm Mechanism or TAGSAM. The mission aims to return a sample of Bennu's surface coating to Earth for study as well as return detailed information about the asteroid and it's trajectory. Credit: NASA's Goddard Space Flight Center

This artist’s concept shows the OSIRIS-REx spacecraft contacting the asteroid Bennu. The mission aims to return a sample of Bennu’s surface coating to Earth for study as well as return detailed information about the asteroid and it’s trajectory. Credit: NASA’s Goddard Space Flight Center

The countdown has begun for NASA’s OSIRIS-REx mission. It is set to visit an asteroid, pick up a sample and bring it back to Earth.

The Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) is a part of NASA’s New Frontiers Program. It is the third mission to be selected as a part of this programme, after Juno to Jupiter and New Horizons to Pluto and beyond. The team behind OSIRIS-REx includes scientists from France, Germany, Italy, the UK, the US and Canada.

The mission was selected to sample the asteroid named 101955 Bennu, commonly called as just Bennu, orbiting the Sun very close to Earth. Unlike typical asteroids, such as the ones floating around in the belt between Mars and Jupiter, Bennu orbits the Sun in an orbit nearly the same as Earth’s. In fact, it’s so close to us that the 500-metre-wide rock’s orbit will bring it within the Moon’s orbit in 2135. It is also classified as a ‘potentially hazardous object’ because it just might smash into Earth someday. But you can breathe easy for now: scientists think that day is at least 300 years away.

Bennu was selected to be the target because it is distinctively black and carbonaceous, an indication that it holds organic compounds we are interested in. Such asteroids are essentially remnants from the early Solar system, debris thrown out during the formation of the Sun and the planets. Their composition is thought to have been unchanged through billions of years. These remnants also suffer minimal space weathering –effects of radiation, high energy rays, and solar wind – and therefore hold a perfect record of conditions that existed when Earth formed. Scientists believe they contain amino acids and sugars, chemical compounds presumed to be the primary building blocks for life on Earth. These compounds have also been found in meteorites before.

All this means that scientists believe analysing the likes of Bennu could give us great insights into the formation of the Solar System and whether space-rocks might have played a significant role in seeding our planet with life.

If that’s true, would we technically be aliens ourselves?

The mission objectives for OSIRIS-REx are:

  • Return and analyse a sample of Bennu’s surface
  • Map the asteroid
  • Document the sample site
  • Compare observations at the asteroid to ground-based observations

The truck-sized spacecraft will be launched into space by an Atlas V rocket on September 8 for a two-year cruise to Bennu.

Halfway through its journey towards Bennu, OSIRIS-REx will prepare to sling past us on September 23 next year, using our planet’s gravity to throw itself toward Bennu. This will increase the speed of the craft from the launch velocity of 19,000 km/hr to nearly 103,000 km/hr. A year after this space-acrobatics, when the probe is about two million km from Bennu, it will slow down to match the asteroid’s speed (101,000 km/hr).

The procedure towards a rendezvous will begin on August 17, 2018. The craft will first start flying in tandem near Bennu before easing into an orbit around it. After reaching the asteroid on March 18, 2019, OSIRIS-REx will begin extensive surveying and mapping of Bennu to determine a location for the sampling of the grey, dusty body.

On July 4, 2020, OSIRIS-REx will descend slowly towards the asteroid, extending a robotic arm named TAGSAM, for Touch-And-Go Sample Acquisition Mechanism. The arm is fitted with a sampler head that looks like a bottle cap. This will hold particles from the asteroid.

When TAGSAM is just a few centimetres away from Bennu, it will let loose a small burst of nitrogen gas to stir up and disturb the surface. The puff will kick up loose grains and small pieces of debris. Some of this will collect in the sampler head. Once that’s done, the TAGSAM arm will retract into the craft, dropping the sample safely in a container to be stowed away for us. The probe will carry enough nitrogen to attempt this exercise thrice, with the arm remaining in physical contact with the asteroid for all of five seconds every time. The craft is capable of carrying up to two kilograms of asteroid material back to Earth.

On March 3, 2021, scientists estimate that OSIRIS-REx will prepare to depart from Bennu, shooting its thrusters out and flying away at the speed of about 1,100 km/hr. After a little over two years of hurling through space, it will reach close to Earth on September 24, 2023, safely holding samples of a tiny, far away body.

When it is close to the planet, the craft will jettison the sample return capsule for re-entry and push away, setting itself in orbit around the Sun. The ejected sample container that is protected in a heat shield will make contact with our atmosphere at a numbing 44,640 km/hr, burning its way towards us. It will continue falling freely till it’s about three kilometres from the surface, when parachutes will deploy for a soft landing. This landing and recovery will take place in the Utah Testing and Training Range, in the desert region in North America, over seven years after the spacecraft’s launch.

Wondrous as the mission sounds, it pays to note that OSIRIS-REx is visiting an asteroid so very close to us and yet returning a sample after seven years. Scientists can’t launch such missions frequently – so they’ll dig as deep into the Bennu sample as they can go with their chemical tools. They’ll be looking for amino acids and other organic compounds, but not for microbes or any kind of primitive life-forms. In fact, the approval for the mission was granted only after scientists could say with some level of cerntainty that microbes do not exist on Bennu. The Planetary Protection Act (Article 9) has heavy restrictions on re-entry vehicles that might contaminate Earth with alien microbes!

A call for naming the asteroid now called Bennu was put out in 2013. The winner was a nine-year-old boy called Mike Puzio, who stated that the craft, with its arm extending out, resembled the Egyptian bird Bennu, thought to be an inspiration for the phoenix. The name was chosen because it aptly went with the theme of the craft named after Osiris, an Egyptian deity himself.

The connections are plenty and interesting, as principal investigator Dante Lauretta noted on his blog three years ago. Osiris, the Egyptian god of afterlife, is said to have sprinkled seeds around the Nile and caused it to flood, thus spreading agriculture. It is believed that asteroids like Bennu possibly seeded life on Earth. Osiris was killed by his brother Set, who shut his body tightly in a coffin and threw it into the Nile. OSIRIS-REx has a capsule that is sealed tight and will be thrown into Earth. Lastly, when Osiris’s body was recovered, Set chopped it up and spread the pieces throughout the world. The samples from OSIRIS-REx will be distributed to the international scientific community for analysis.

In its initial days, the mission was just called OSIRIS. Then, when Lauretta’s team decided to up the ante and have OSIRIS sample the asteroid’s regolith – surface rock of a body – they decided to add a form of “regolith explorer” to it. Remembering how the dinosaurs died due to an asteroid impact, Lauretta added “REx” to the name. It makes for good irony: now a dinosaur is rushing at enormous speeds towards an asteroid.

Sandhya Ramesh is a science writer focusing on astronomy and earth science.