NASA announces Mars 2020 rover payload

Image: NASA/JPL-Caltech
Image: NASA/JPL-Caltech

On July 31, NASA announced the roster of instruments that would hitch a ride on board its planned rover to the red planet in 2020. John Grunsfeld, astronaut and associate administrator for the NASA Science Mission Directorate, Headquarters, Washington, said the instruments would extend the search for life in Mars’s past, conduct geological and environmental investigations to that end, equip it to cache martian material for future explorers to bring back to Earth, and conduct studies that will help the agency land humans on Mars.

Michael Meyer, lead scientist with the Mars Exploration Program, detailed the instruments that would go on board the rover. Going from mast to the body and then to the arm, he laid out seven major instruments developed by over 50 institutions from around the world. Meyer said their guiding principle is that no measurement will be done by only one instrument, that whether it was the chemistry, mineralogy or geology that was being studied, the instruments would overlap, provide multiple perspectives on readings and help constrain error.

The mast would hold the cameras called Mastcam Z and SuperCam. Mastcam Z will be a binocular with zoom capable of rapidly developing terrain models. According to Meyer, the Curiosity rover is slowed down by having to reassess its surroundings once every 10 m for rocky outcrops or surfaces that might threaten it. Mastcam Z will be equipped to plot out greater distances at once. SuperCam, with a significant contribution from France, is the 2020 rover’s counterpart of Curiosity’s ChemCam, which ionizes martian soil samples and studies the missions for their mineral composition. Additionally, SuperCam will also boast a visible and near-infrared spectrometer to make observations at those wavelengths. It will be a remote-sensing instrument to help make important decisions about soil composition and the presence of organic material.


The rover’s body will hold instruments called MOXIE, MEDA and RIMFAX, and MOXIE takes the cake for innovation. It will attempt to extract carbon dioxide from Mars’s atmosphere, break it down and produce pure oxygen. Meyer said that the oxygen could comprise rocket fuel for future human explorers. However, Bill Gerstenmaier, associate administrator for the NASA Human Exploration and Operations Directorate, implied that that claim was exaggerated, saying scientists would first study at what rate and efficiency oxygen could be produced and if its presence could pose any risks.

MEDA, from Spain, would be the on-board weather station, providing data on atmospheric conditions. RIMFAX will give the 2020 rover the ability to ‘see’ below Mars’s surface. It’s a ground-penetrating radar that can go up to 0.5 km downward and and help connect outcrops on the surface with geological formations beneath them.

Two instruments will ride the rover’s arm: PIXL, the interfacing instrument that tells scientists where the action is at smaller scales based on samples the other instruments have analysed, and SHERLOC, a deep-UV instrument adept at studying organic material.

Even though all instruments will be capable of performing multiple analyses, the flow of ‘work’ according to Meyer is roughly ordered as: mast instruments look around the landscape for interesting things, mineralogies that might be best at preserving biosignatures and recent outcrops; arm instruments study samples at finer scales and look at features that might’ve attracted microbial growth in the past; then, based on data, scientists decide whether they want to drill and cache that sample for posterity.

Mars-2020 is being envisaged as Curiosity’s next step with bifurcated goals: landing humans on Mars by studying local geological and radiological properties, and looking for life in its past and helping conduct more sophisticated studies on soil samples.

Like with MOXIE, Meyer explained that the caching of samples would also be proof-of-concept: NASA definitely intends to cache samples but isn’t yet sure what it will do with them. Grunsfeld quoted Carl Sagan to say that if they did find signs of life, they’d also have to muster extraordinary evidence to back up their claim – evidence that could only be established if the samples were subjected to tougher tests on Earth. Meyer concluded by adding that the one-metric-ton rover would be landed on Mars the same way Curiosity was – with the sky-crane.

New category: Exoplanets

Using a network of telescopes scattered across the globe, including the Danish 1.5-m telescope at ESO La Silla (Chile), astronomers  discovered a new extrasolar planet significantly more Earth-like than any other planet found so far. The planet, which is only about 5 times as massive as the Earth, circles its parent star in about 10 years. It is the least massive exoplanet around an ordinary star detected so far and also the coolest. The planet most certainly has a rocky/icy surface. Its discovery marks a groundbreaking result in the search for planets that support life.
An artist’s impression of an icy exoplanet. Image: Wikimedia Commons

Of late, telescopes like Kepler, Spitzer and ALMA are revealing new things about exoplanets as much as they’re exposing how clueless we are about their origins. Unlike in the search for life, where our only precedents are terrestrial, the search for and study of exoplanet systems is aided by Kepler’s revelation of hundreds of them, in a variety of flavors. And the more of them we discover, the more it becomes evident that in many ways the Solar System is actually an outlier, and that subjecting our stellar neighborhood to more probing is only going to reveal so much about the incomparable world outside. Each discovery is an opportunity for astronomers to revisit some detail or other. Like in the Banach-Tarski paradox, a dismantled theory is pieced back together to predict different things with a twist or two. Needless to say, it’s an exciting time to be a planetary scientist – or an interested blogger. To keep track of developments, The Last Why has a new category called ‘Exoplanets’. The eight posts already filed in it are linked to below, with more to come. Enjoy the ride!

  1. Why do tilted/eccentric orbits form?
  2. Kepler data reveals a frost giant
  3. Looking for life? Look for pollution.
  4. Studying our primal horizons at the Kuiper belt
  5. What life on Earth tells us about life ‘elsewhere’
  6. Rocky exoplanets only get so big before they get gassy
  7. The secrets of how planets form
  8. Interactions between a planetary system and an FFP: A fuzzy approach

Why do tilted/eccentric orbits form?

For all its mysteries, the Solar System is uniquely ideal in many ways. For one, while it has rocky inner planets and giant, gassy outer ones, astronomers have found that elsewhere, massive exoplanets often orbit close to their stars, as if they formed at a greater distance and then moved in. For another, the orbits of the planets around the Sun are nearly circular and on the same plane. This is unlike what the Kepler space telescope has found in other star systems, where exoplanets often have eccentric orbits and orbits that are tilted with respect to the star’s equator. A July 31 paper in Nature adds one more system to this difference, but this time with some information about why eccentric/tilted orbits could form. Eric Jensen (Swarthmore College) and Rachel Akeson (NASA) discuss the binary star system HK Tauri, whose stars are one and four million years old with 386 AU between them. More importantly, one star, HK Tau B, has a disk of gases and dust around itself that, when viewed from Earth, appears to be edge-on, masking the starlight and making for easier imaging in visible light. Such a disk is called a protoplanetary disk because it contains the materials from which planets form.

The other star, HK Tau A, is also inclined as seen from Earth but not edge-on, so the bright starlight bleaches observations made in visible light. So Jensen and Akeson observed it in millimeter-wavelength light using the ALMA telescope in Chile and calculated its disk’s rotation rate (specifically, by observing Doppler effects on the carbon-monoxide emission lines). HK Tau A is inclined at 43° ± 5°; HK Tau B is inclined at 85° ± 1°. Depending on which direction the disks are rotating in, Jensen & Akeson find that they’re inclined relative to each other at at least 60° and at most 68° (± 3° for both). So planets forming in their protoplanetary disks could end up with eccentric and tilted orbits around their individual stars as a result of being perturbed by gravitational effects from their neighbor. As Jensen told Centauri Dreams: “Our results show that the necessary conditions exist to modify planetary orbits and that these conditions are present at the time of planet formation, apparently due to the formation process of a binary star system. We can’t rule other theories out, but we can certainly rule in that a second star will do the job.”


Jensen, E. & Akeson, R., Misaligned protoplanetary disks in a young binary star system, Nature 511, 567–569 (31 July 2014). doi:10.1038/nature13521

Curious Bends – commoner panthers, space diplomacy, big data sells big cars and more

Curious Bends is a weekly newsletter about science, tech., data and India. Akshat Rathi and I curate it. You can subscribe to it here. If have feedback, suggestions, or would just generally like to get in touch, just email us.

1. Why the GM debate in India won’t abate

It is a sign of its inadequacy that the debate on genetically modified crops in India is still on, with no end in sight. Although public consensus is largely polarised, the government has done its bit to postpone resolution. For one, decisions on GM crops are made as if they were “technical answers to technical questions”. For another, no formal arena of debate exists that also addresses social anxieties. (8 min read)

2. One foot on Earth and another in the heavens

Camera traps installed by the Wildlife Conservation Society of India have shown that about one in ten of all leopard images belong to black leopards (that is, black panthers). These melanistic big cats have been spotted in wildlife reserves in Kerala and Karnataka, and seem commoner in the wetter forests of the Western Ghats. In fact, written records of sightings in these parts date from 1879, and could aid conservation efforts in a country that lost its cheetahs in 1960. (2 min read)

3. One foot on Earth and another in the heavens

For smaller and middle income nations, strengthening institutional and technical capacity on the ground might be a better option than to launch satellites because more than vanity, the choice makes them better positioned to gather useful data. And if such a nation is in South Asia, then India’s planned SAARC satellite could make that choice easier, providing a finer balance between “orbital dreams and ground realities”. (5 min read)

+ The author, Nalaka Gunawardene, is a journalist and science writer from Colombo, Sri Lanka.

4. Do big car-makers know their way around big data?

When sales slumped, Mahindra & Mahindra, an Indian car-maker, used data gleaned from the social media to strip its former best-selling XUV500 model of some features and sell it cheaper. The company declined to give further details. This isn’t unique—big car-makers around the world are turning to big data to widen margins. But do they know how best to use the data or is it just that putting the squeeze on this lemon is a fad? (6 min read)

5. A geothermal bounty in the Himalayas

As the developing world edges toward an energy sufficiency crisis, scientists, environmental conservationists and governments get closer to a Mexican standoff. This is no better highlighted than with the gigawatts of geothermal energy locked up in the Himalayas. A 20-MW plant could “save three million litres of diesel”, $2 million and 28,000 tons of carbon dioxide in northern India per year. Why isn’t it being used? (2 min read)

Chart of the week

“Both [female genital mutilation and child marriage] stem from deeply rooted social norms which can only be changed by educating parents about the harm they cause. Making foreign aid conditional on results gives governments an extra incentive not just to pass laws, but to enforce them. Police and women’s activists in some countries have set up phone hotlines and safe houses for victims or girls at risk. Most important … is to make sure that girls go to school and finish their studies.” The Economist has more.


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Accurate measurement of exoplanet radius

Using data from NASA's Kepler and Spitzer Space Telescopes, scientists have made the most precise measurement ever of the size of a world outside our solar system, as illustrated in this artist's conception. Image: NASA/JPL-Caltech

Image: Imaginative illustration of Kepler 93b’s diameter being measured. Credit: NASA/JPL-Caltech

Using both the Kepler and the Spitzer space telescopes, scientists from NASA have made the most precise measurement of an exoplanet’s radius yet. Kepler 93b, which orbits a dim star 300 ly away, has a diameter of 18,800 km, give or take 240 km. “The measurement is so precise that it’s literally like being able to measure the height of a six-foot tall person to within three-quarters of an inch – if that person were standing on Jupiter,” said Sarah Ballard, an astronomer at the University of Washington and lead author of a paper in The Astrophysical Journal that describes the findings, in a JPL statement.

Kepler 93b is a super-earth, a common class of planets in the Milky Way but missing in the Solar System. Super-earths weigh between the masses of Earth and Uranus. Scientists were able to its radius to within 240 km by first using the Kepler space telescope to record how much of starlight the exoplanet blocked when transiting across its face. Next, they used precise measurements of seismic waves moving within the star’s interior to calculate how much light it gave off and its radius. This technique falls within the field of astroseismology that has been used since the early 2000s. Astroseismic measurements are effective when the observatories have a long baseline, long observing time and high photometric precision.

The scientists were aided in their work by Kepler 93 being a cool dwarf star whose brightness varies less often and strongly enough to help constrain planetary transit and seismic measurements.

Then, the Spitzer space telescope used its Infrared Array Camera, or IRAC, to confirm that what Kepler was observing wasn’t a false-positive. It did this by using the fact that no matter which wavelength a transiting exoplanet is observed in, its transit depth will be the same. The transit depth is the ratio of the size of a planet’s disk to the star’s disk. So while Keplre measures this ratio in visible light, the IRAC will measure it in infrared light. To rule out a false-positive, the two measurements have to be the same.

The IRAC measurement was improved using a method developed in 2011, which checks how light falls on individual pixels in the camera. The scientists used Kepler 93b as a test bed, examining the exoplanet’s seven transits recorded between 2010 and 2011 in detail. Based on its mass – 3.8-times Earth’s – and radius, it was found to be made mostly of iron and rock, its biggest similarity to Earth. However, it orbits its star at a distance almost 19 times shorter than that between us and our Sun, making its surface too hot for life at 760 degrees Celsius.

Spitzer lost its coolant, and therefore the sensitivity of some of its instruments, in 2009. A telescope that measures heat coming in from various regions of the cosmos must have little heat of its own, which the cryogen ensured. Once it ran out, the temperature inside the telescope rose by 29 degrees Celsius, too warm for longer wavelength instruments but still cold enough for shorter wavelength ones like IRAC. The precision of the Kepler 93b measurement will give hope for future studies to understand why and how super-earths form, and instruments like IRAC will play an important role in that scenario.



Sarah Ballard et al., Kepler 93b: A terrestrial world measured to within 120 km, and a test case for a new Spitzer observing mode, 2014 ApJ 790 12 doi:10.1088/0004-637X/790/1/12 (pre-print)

JPL press releaseThe Most Precise Measurement of an Alien World’s Size, July 23, 2014

Hearing test, radiation-resistant cells, sign language and more

Curious Bends is a weekly newsletter about science, tech., data and India. Akshat Rathi and I curate it. You can subscribe to it here. If have feedback, suggestions, or would just generally like to get in touch, just email us.

1. Poor children deserve better hearing tests; an Indian entrepreneur may have the solution

An estimated 63 million people in India suffer from hearing problems. But children are not tested for such impairment at a young age because of the costs of testing. Early detection and intervention is crucial for improving the difficulties with cognition and language skills. Now, a Bangalore-based inventor has come up with a solution that sharply lowers the cost of testing if a newborn can hear properly. (3 min read)

2. What makes cells resistant to radiation?

Radiation can damage cell’s DNA, and sometimes make them cancerous. But not all cells are affected by such radiation. Previously, it was thought that such ability was down to the DNA repair mechanisms in place in every one of them, but a new study shows that cells have more weapons to fight this invisible attack. (2 min read)

3. What sign language teaches us about the brain

As she took a course to learn sign language, a question kept nagging this neurobiologist: does the brain treat the visual language differently from spoken languages? Turns out, for the most part, they don’t. And yet brain studies of deaf people who use sign language helps bust a few myths about how our brains work. (5 min read)

+ The author of this piece, Sana Suri, is a neurobiologist at the University of Oxford.

4. Another biotech startup accelerator opens up in Bangalore. Can it deliver?

India’s biotech industry is supposed to be undergoing a boom. It was projected that revenues would reach $5 billion by 2009, but that hasn’t happened yet. Industry watchers remain optimistic, claiming that revenues will reach $100 billion by 2020. Can a startup accelerator help achieve this dream? (5 min read)

5. BRICS can boost their research by setting up collaborations, but there seems to be no will

The recent BRICS summit in Brazil saw the launch of the New Development Bank, which has been setup to rival the World Bank and the International Monetary Fund. But there was little progress on setting aside joint funds to boost scientific collaboration. There is a huge potential here but no one is interested in tapping it. (2 min read)

Chart of the week

It has been a terrible week for the civilian aviation industry with Malaysia Airlines Flight 17 shot down over Ukraine and an ongoing investigation of Air Algerie Flight 5017 that crashed in Mali. Vasudevan Mukunth (one of the curators of Curious Bends; a.k.a. me) has collected the data of all such past events in one interactive chart.


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Science Quiz – July 28, 2014

Every week, I create a science quiz for The Hindu newspaper’s In School product. It consists of 10 questions and only developments from the week preceding its day of publication (Monday). The answers are at the end.

  1. What’s a haboob?
  2. American biologists tracked ____ ______ over 15 years. On July 25, they announced that their species could be protected from collisions from ships moving in waters along the western coast of North America, contributing to their long-term survival. Fill in the blanks.
  3. In the last last two decades, over 1,500 planets outside the Solar System have been found. In the week of July 21, 2014, astronomers said that life on these planets would find it easier to evolve if they had ______, which would keep surface temperatures from varying too much between day and night. Fill in the blank with the name of a visible object found commonly in Earth’s atmosphere, with types like uncinus, spissatus, nebulosus, congestus, etc.
  4. Researchers who were studying the behavior of dogs found that man’s best friends also experience ________ like humans do, implying that this emotion may not require complex minds. Fill in the blank.
  5. Paleontologists have found 70-million year old footprints of ____________ ___ in Canada. The prints show three pairs of limbs moving parallel to each other, suggesting that these reptiles might have hunted in packs. Fill in the blanks with the name of a dinosaur whose name in Latin means “king lizard”.
  6. If a group of scientists from America and France are to be believed, the evolution of the sizes and shapes of human-made airplanes are mimicking the evolution of the sizes and shapes of what?
  7. According to a report published on July 22, 2014, which animal (with the nomenclature Loxodanta africana) has the world’s most sensitive nose, possessing over 2,000 genes to sense smells (as opposed to humans’ about 400)?
  8. The spots on a _____ _______ are masked by their black fur, making it harder to tell them apart or document their numbers. According to National geographic, however, these animals are less rare than supposed, having been found to be particularly common in the Anshi-Dandeli tiger reserve, Karnataka. Fill in the blanks.
  9. Twenty years ago, in July 1994, the comet Shoemaker-Levy 9 broke apart and collided with the _______, providing the astronomers with their first chance to observe to two extraterrestrial bodies colliding within the Solar System. The comet is also unique because it was found to be orbiting the planet instead of the Sun. Fill in the blank with the name of the planet.
  10. July 25 was the 94th birth anniversary of this British biophysicist who made great important contributions to the study of molecular structures. Around 1953, she helped James Watson and Francis Crick discover the double-helix sructure of DNA, a watershed moment in the history of molecular biology. Name her.


  1. An intense dust storm that occurs in arid regions of the world, also known as a sandstorm. They are carried by winds moving into a thunderstorm.
  2. Blue whales
  3. Clouds
  4. Jealousy
  5. Tyrannosaurus rex
  6. Birds
  7. African bush elephant
  8. Black panther
  9. Jupiter
  10. Rosalind Franklin

No country for new journalism

(Formatting issues fixed.)

TwitterNgoodThrough an oped in Nieman Lab, Ken Doctor makes a timely case for explanatory – or explainer – journalism being far from a passing fad. Across the many factors that he argues contribute to its rise and persistence in western markets, there is evidence that he believes explainer journalism’s historical basis is more relevant than its technological one, most simply by virtue of having been necessitated by traditional journalism no longer connecting the dots well enough.

Second, his argument that explainer journalism is helped by the success of digital journalism takes for granted the resources that have helped it succeed in the west and not so much in countries like India.

So these points make me wonder if explainer journalism can expect to be adopted with similar enthusiasm here – where, unsurprisingly, it is most relevant. Thinking of journalism as an “imported” enterprise in the country, differences both cultural and historical become apparent between mainstream English-language journalism and regional local-language journalism. They cater to different interests and are shaped by different forces. For example, English-language establishments cater to an audience whose news sources are worldwide, who can always switch channels or newspapers and not be worried about running out of options. For such establishments, How/Why journalism is a way to differentiate itself.

Local v. regional

On the other hand, local-language establishments cater to an audience that is not spoiled for options and that is dependent profoundly on Who/What/When/Where journalism no matter where its ‘reading diaspora’. For them, How/Why journalism is an add-on. In this sense, the localism that Ken Doctor probes in his piece has no counterpart. It is substituted with a more fragmented regionalism whose players are interested in an expanding readership over that of their own scope. In this context, let’s revisit one of his statements:

Local daily newspapers have traditionally been disproportionately in the Who/What/When/Where column, but some of that now-lost local knowledge edged its ways into How/Why stories, or at least How/Why explanations within stories. Understanding of local policy and local news players has been lost; lots of local b.s. detection has vanished almost overnight.

Because of explainer journalism’s reliance on digital and digital’s compliance with the economics of scale (especially in a market where purchasing power is low), what Doctor calls small, local players are not in a position to adopt explainer journalism as an exclusive storytelling mode. As a result of this exclusion, Doctor argues that what digital makes accessible – i.e. what is found online – often lacks the local angle. But it remains to be seen if this issue’s Indian counterpart – digital vs. the unique regional as opposed to digital vs. the small local – is even likely to be relevant. In other words, do smaller regional players see the need to take the explainer route?

Local-level journalism (not to be confused with what is practiced by local establishments) in India is bifocal. On the one hand, there are regional players who cover the Who/What/When/Where thoroughly. On the other, there are the bigger English-language mainstreamers who don’t each have enough reporters to cover a region like India thanks, of course, to its profuse fragmentation, compensating instead by covering local stories in two distinct ways:

as single-column 150-word pieces that report a minor story (Who/What/When/Where) or

as six-column 1,500-word pieces where the regional story informs a national plot (How/Why),

—as if regional connect-the-dots journalism surfaces as a result of mainstream failures to bridge an acknowledged gap between conventional and contextualizing journalism. Where academicians, scholars and other experts do what journalists should have done – rather, in fact, they help journalists do what they must do. Therefore, readers of the mainstream publications have access to How/Why journalism because, counter-intuitively, it is made available in order to repair its unavailability. This is an unavailability that many mainstreamers believe they have license to further because they think the ‘profuse fragmentation’ is an insurmountable barrier.

There’s no history

The Hindu and The Indian Express are two Indian newspapers that have carved a space for themselves by being outstanding purveyors of such How/Why journalism, and in the same vein can’t be thought of as having succumbed to the historical basis that makes the case for its revival—“Why fix something that ain’t broken?”. And the “top-drawer” publications such as The New York Times and The Washington Post that Doctor mentions that find a need to conspicuously assert this renewal are doing so on the back of the technology that they think has finally made the renewal economically feasible. And that the Times stands to be able to charge a premium for packaging Upshot and its other offerings together is not something Hindu or Express can also do now because, for the latter couple, How/Why isn’t new, hasn’t been for some time.

Therefore, whereupon the time has come in the western mainstream media to “readopt” explainer journalism, its Indian counterpart can’t claim to do that any time soon because it has neither the west’s historical nor technological bases. Our motivation has to come from elsewhere.

Dying in a finite universe

In his book Infinite In All Directions (2002), Freeman Dyson, one of the tallest intellectual giants of our times, attempts to rescue eschatology from the specious grip of religion and teleology with a mix of scientific reasoning and informed speculation. During this, when describing the big crunch, which is one way our universe could end, he moves smoothly from the rational track he has been sprinting on to a less exact but more pertinent and romantic description. In his words,

There is a great melancholy in the picture of a finite universe, its force spent, its days of passion over, counting the hours remaining before it slides into oblivion. What will our last poets sing, whoever they may be, human or alien, as they watch the stars crowding together and streaming faster and faster across the imploding sky? Perhaps in their final moments they will remember the words of our contemporary, Ivor Gurney, echoing down the eons from the springtime of our species:

The songs I had are withered
or vanished clean,
Yet there are bright tracks
Where I have been,
And there grow flowers
For others’ delight.
Think well, O singer,
Soon comes night.

I wonder if the universe will make this transition just as seamlessly, and the twilight of starstuff will prove to be just as pleasing, should it happen. Then again, to share Dyson’s conviction is to embrace naturalism for that’s all the beauty that we will see, and there is hope that it will be inexhaustible. Again, in his words and from the same book,

No matter how far we go into the future, there will always be new things happening, new information coming in, new worlds to explore, a constantly expanding domain of life, consciousness and memory.

Kepler data reveals a frost giant

I’ve been most fascinated lately by studies of planet formation. Every small detail is like that one letter in the crossword you need to fill all the other boxes in, every discovery a cornerstone that holds together a unique piece of the universe. For example, using just the find that the exoplanet Beta Pictoris b has a very short day of eight hours, astronomers could speculate on how it was formed, what its density could be, and how heavy it could get over time. And it isn’t surprising if a similar tale awaits telling by Kepler 421b, an exoplanet some 1,000 ly from Earth toward the constellation Lyra. Its discovery was reported on July 17, a week ago. And its pièce de résistance is that it has a long year, i.e. orbital period, of 704 days.

Illustrating the transit technique. The technique applies only when the planet can be seen head on against the background of its star. Image:

Image: Illustrating the transit technique. The Kepler telescope looks for the drop in brightness in its search for exoplanets. The technique applies only when the planet can be seen head on against the background of its star. Credit:

To have such a long year, it must be orbiting pretty far from its star – Kepler 421 – which in turn should’ve made it hard to discover. The NASA Kepler space telescope spots exoplanets by looking for the dip in a star’s brightness as the planet moves in front of it, called a transit. Because of Kepler 421b’s high orbital period, it transited its central star only twice in the four years Kepler was looking at it. Together with its orbital eccentricity – i.e. how elliptic its orbit is – Kepler had only a 0.3% chance of spotting it on its way around the star. In fact, 421b has the longest year for any known exoplanet discovered using the transit technique. This means we need to start considering if the M.O. isn’t good enough to spot exoplanets with large orbital periods, a class of planets that astronomers have been looking for. On the other hand, now that 421b has been spotted and studied to some extent, astronomers can form impressions of its history and future.

The frost line

For starters, they were able to deduce the planet’s size based on how much starlight it blocked and the shape of its orbit from how much light it blocked during each full transit. The readings point to 421b being like Uranus, with radius four times Earth’s, density at least 5 g/cc, and an eccentric orbit. Being like Uranus also means a surface temperature of -90 degrees Celsius (183 kelvin). This is plausible because 421b is 1.2 times as far from its star as Earth is from the Sun, and its star is a dimmer orange dwarf.

These wintry conditions are found beyond a star’s frost line, an imaginary line marking the distance beyond which space is cold enough to cause hydrogen-based molecules to condense into icy grains. So planets orbiting beyond this distance are also icy. Kepler 421b is likely the first exoplanet astronomers have found (using the transit technique) orbiting a star beyond its frost line. In other words, this might be our first exoplanet that’s an ice giant – “might” because 421b hasn’t been independently observed yet.

Not surprisingly, the frost line also marks a more significant boundary in terms of planet formation. Though observations made by Kepler are starting to show that the Solar System is a surprisingly unique planetary system, it’s still the one we understand best and use to analogize what we finds in other worlds. Astronomers believe planets in the system formed out of a disk of matter surrounding a younger Sun. The inner Earth-like (telluric) planets formed when rocky matter started to clump together and “fall out” of this disk. The outer gaseous planets, beyond the frost line, formed when icy grains stuck together to form watery planetary embryos.

In this artist's conception, gas and dust-the raw materials for making planets-swirl around a young star. The planets in our solar system formed from a similar disk of gas and dust captured by our sun. Credit: NASA/JPL-Caltech


Image: In this artist’s conception, gas and dust-the raw materials for making planets-swirl around a young star. The planets in our solar system formed from a similar disk of gas and dust captured by our sun. Credit: NASA/JPL-Caltech

The prevailing belief is that planets take at least three million years to form. In the same period, the central star is also evolving – in this case, Kepler 421 is a K-class star becoming brighter – and the amount of material available in the protoplanetary disk is diminishing because planets are feeding off it. Consequently, the frost line is on the move. Calculations by the astronomers who discovered 421b find the exoplanet to be now where the system’s frost line might’ve been three million years ago.

The sedate giant

Right now, we’ve a lot of letters in the crossword. Piecing them together, we can learn the following:

  1. If a beyond-the-frost-line gas giant is as big as Uranus but not as big as Jupiter, it’s possible that not enough material was available when it started to form, rendering it a latecomer in the system
  2. The abundance of material required to form Jupiter-sized planets makes smaller worlds likelier than larger ones, and in fact implies worlds like 421b should be less unique than Kepler makes it seem (a 2013 study cited by the discoverers suggests that there might actually be a pile-up of planets transiting at the frost line of their stars)
  3. If the planet had to have formed behind its star’s frost line, and the frost line was three million years ago where the planet is now, the planet could be around three million years old – assuming it hasn’t moved around since forming
  4. 421b is very Uranus-like; if it has to be a rocky world, its mass has to be 60 times Earth’s, pointing at an improbably massive protoplanetary disk within one or two AU of a star – something we’re yet to find

#3 warrants a comparison with the Solar System’s history, especially Jupiter’s. Jupiter didn’t form where it is right now, having possibly moving toward and away from the Sun as a result of gravitational interactions with other planets that were forming. During its journeys, its own gravitational pull could’ve tugged on asteroid belts and other free-floating objects, pulling them out of one location and depositing them in another. Contrarily, 421b appears to have been far more sedate, probably not having moved at all due to its youth and isolation. If only it had moved inward, like Jupiter eventually did, its orbital period would’ve been shorter and Kepler would’ve have spotted it easier.

The confusion Jupiter might've caused during its journey through Middle Earth. Image:

Image: The confusion Jupiter might’ve caused during its journey through a nascent Solar System. Credit:

Another comparison can be made with Beta Pictoris b, the other exoplanet mentioned at the beginning of this piece, the one with the eight-hour-long days. Younger planets spin faster because they still have the angular momentum they acquired while accumulating mass before slowing down in time. Heavier planets also spin faster because they have more angular momentum to conserve. Similarly, we might be able to find out more about Kepler 421b’s past by uncovering its spin rate and getting a better estimate of its mass.

Anyway, a simple piecing together of facts and possibilities tells us – at least me – this much. Astronomers have one more awesome fact to take away: as the finders of 421b write in their pre-print paper, “the first member of this missing class of planets” has been found, and that means more astronomy to look forward to!



Discovery of a transiting planet near the snow line, Kipping et al, arXiv:1407.4807 (accepted in The Astrophysical Journal)