Archive for the ‘Exoplanet Science’ Category

Christian Ready's video explainer about exoplanet Kepler 22b

December 22, 2011 3 comments

My friend Christian Ready, a web developer who used to work on the Hubble Space Telescope mission, has made a clear, well-paced, and visually captivating explainer video about “the discovery of Kepler 22b, a planet orbiting a star not unlike our own sun at a distance where life can thrive.” (This is the finding that was announced BEFORE the more recent announcement of Kepler 20e and 20f, Earth-sized planets that are not in the so-called “habitable zone” of their star.) You can see other videos by Christian on his YouTube channel.

OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.



NASA Goddard's Marc Kuchner talks about alien planets on public TV

December 20, 2011 Leave a comment

You may have heard the big exoplanet news today:

NASA’s Kepler mission has discovered the first Earth-size planets orbiting a sun-like star outside our solar system. The planets, called Kepler-20e and Kepler-20f, are too close to their star to be in the so-called habitable zone where liquid water could exist on a planet’s surface, but they are the smallest exoplanets ever confirmed around a star like our sun.

In the general spirit of the day, here is some more planet talk — from NASA astrophysicist Marc Kuchner, who recently appeared on Maryland Public Television to discuss the latest research on planets around other stars.

OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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Highlights of this week's exoplanet feast at Goddard

October 21, 2011 Leave a comment
Spiral signpost of planets

Spiral signpost of planets

This week, it’s been a feast of exoplanet science at Goddard, which hosted the Signposts of Planets meeting Oct. 18-20. The three-day conference gathered an international crowd of observers, computer modelers, and instrument builders to explore the relationship between exoplanets and the circumstellar disks in which they form.

Circumstellar what?

Circumstellar simply means “disks of gas and dust around a star or stars.” Astronomers have discovered some 687 planets around other stars, but ironically they rarely are able to “see” one directly. What the Hubble telescope and other instruments see are dusty disks.

Circumstellar disks are the “signposts of planets” referenced by the name of the conference. Want to find planets? Look for dusty disks.

Here is Goddard astrophysicist and Signpost meeting organizer Marc Kuchner explaining the lowdown on circumstellar disks, back when we only knew of about 400 extrasolar worlds:

The conference produced some show-stoppers in terms of new discoveries announced. Four were the subject of press releases:

Spiral signposts
At the meeting, Goddard astronomer Carol Grady announced the discovery of a type of exoplanet telltale predicted but never actually imaged before. In some circumstellar disks, the tug of a planet’s gravity can create subtle spiral features in the gas and dust. That is good news, because it means that disks with spirals could lead astronomers to planets.

“What we’re finding is that once these systems reach ages of a few million years, their disks begin to show a wealth of structure — rings, divots, gaps and now spiral features,” said John Wisniewski, a collaborator at the University of Washington in Seattle. “Many of these structures could be caused by planets within the disks.”

The newly imaged disk surrounds SAO 206462, a star located about 456 light-years away in the constellation Lupus.

Baby planet

Baby planet

Baby planet
Also at the conference, astronomer Adam Kraus explained how he used the mammoth Keck telescopes on Mauna Kea in Hawaii to image an infant planet. “LkCa 15 b is the youngest planet ever found, about 5 times younger than the previous record holder,” said Kraus, who is based at the University of Hawaii’s Institute for Astronomy.

Kraus did the work using a technique called interferometry, which allows a telescope to achieve the detail-resolving power equivalent to that of a much larger telescope.

Cool findings
In another report at the Signpost meeting, astronomer Kevin Luhman of Penn State University described his observations of a star with a cool planet-like companion. The object, a gaseous not-quite-a-star called a brown dwarf, has an outer temperature described as comparable to “a hot summer day in Arizona.”

Coolest brown dwarf ever

Coolest brown dwarf ever

Luhman commented:

“Its mass is about the same as many of the known extra-solar planets — about six to nine times the mass of Jupiter — but in other ways it is more like a star. Essentially, what we have found is a very small star with an atmospheric temperature about cool as the Earth’s.”

OK, not quite a planet — but not quite a star either. Brown dwarfs lie in between. But they lie along a spectrum of objects that exoplanet researchers study.

Ever since brown dwarfs first were discovered in 1995, astronomers have been trying to find new record holders for the coldest brown dwarfs because these objects are valuable as laboratories for studying the atmospheres of planets with Earth-like temperatures outside our solar system.

Comet storm

Comet storm

And last but not least, comet storms!

NASA’s Spitzer Space Telescope has detected signs of icy bodies raining down in an alien solar system. The downpour resembles our own solar system several billion years ago during a period known as the “Late Heavy Bombardment,” which may have brought water and other life-forming ingredients to Earth.

Carey Lisse, senior research scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland., announced the finding at the Signposts conference. The research will be published in the Astrophysical Journal.

OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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Extra! Extra! NASA's Kepler mission discovers possible 'earthlike' planets. What's that mean anyway?

February 2, 2011 2 comments

artist view of solar system around another star

The big NASA news of the day is that the Kepler mission has discovered planets that are about the size of our own and may have similar conditions for life. Or as the press release explains:

“NASA’s Kepler mission has discovered its first Earth-size planet candidates and its first candidates in the habitable zone, a region where liquid water could exist on a planet’s surface. Five of the potential planets are near Earth-size and orbit in the habitable zone of smaller, cooler stars than our sun.”

Recently a Kepler team acientist and famous exoplanet hunter, David Charbonneau, stopped by Goddard to give a talk and gogblog got a chanvce to ask a few dumb questions. Starting with: “What do you means by earthlike planet? And what is a super Earth?”

OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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Gogblogcast #5: Marc Kuchner and the Search for Other Earths

January 20, 2011 Leave a comment

Marc Kuchner is an astrophysicist at Goddard Space Flight Center who studies planetary systems around other stars. As he explains in this video, the trouble is that when you point a telescope — even one as powerful as the Hubble Space Telescope — at a star with a planetary system, you can’t see the actual planets very clearly. At best you see a glowing dot.

But what you CAN see very clearly is the thin dusty disk that occupies a vast volume of space around the star. Our solar system has one, too: It’s called the zodiacal cloud.

Marc and his students — most notably, Christopher Stark, now at the Carnegie Institution for Science in Washington, D.C. — have developed computer simulations of planetary dust. This is what the simulations show: Although it may be some time before we have a space telescope powerful enough to directly image the face of an alien planet, we should be able to detect the presence of planets by the effects they have on dusty disks. Most likely those planetary telltales will be structures such as rings and dimples.

Want to know more about dust simulations? See a previous gogblog post and the computer visualization below for the details.

By the way, when Marc mentions during the interview that there are “about 400 planets known,” it was accurate. But since this interview was recorded, the count has risen to 500!

OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.



WASP-12b: Shine on you crazy diamond planet

December 8, 2010 2 comments

Artist's concept of a carbon planet with a tar covered surface. A meteor impact has exposed a diamond layer in the planet's interior. For permission to reproduce this figure, please contact Lynette R. Cook, Credit: Lynette Cook (

In this artist's concept of a tar-covered carbon planet, a meteor impact has exposed a diamond layer in the planet's interior. For permission to reproduce this figure, please contact Lynette R. Cook at Credit: Lynette Cook (

“There is no use trying, said Alice; one can’t believe impossible things. I dare say you haven’t had much practice, said the Queen. When I was your age, I always did it for half an hour a day. Why, sometimes I’ve believed as many as six impossible things before breakfast.”

This just in from our Department of Impossible Things: carbon-soaked planets harboring rock formations glittering with diamonds instead of quartz or other silicate minerals common on Earth. Imagine dark gray plains of graphite. Bubbling pools of tar. A smoggy methane atmosphere.

Scientists today report using the Spitzer Space Telescope to discover the carbon-rich recipe of a previously known exoplanet called WASP-12b. A press release today from Jet Propulsion Laboratory has more details:

Astronomers have discovered that a huge, searing-hot planet orbiting another star is loaded with an unusual amount of carbon. The planet, a gas giant named WASP-12b, is the first carbon-rich world ever observed. The discovery was made using NASA’s Spitzer Space Telescope, along with previously published ground-based observations.

Here at Goddard, exoplanet researcher Marc Kuchner received the news with barely concealed glee. In years past, his work contributed to establishing the hypothetical existence of carbon planets. The WASP-12b observations confirm it.

The implications are exotic. Weird things happen when the ratio of carbon to oxygen in a planetary system crosses the tipping point — that being a ratio greater than 1 to 1.

“When the relative amount of carbon gets that high, it’s as though you flip a switch, and everything changes,” Kuchner explains. “Everything would be different — like imagine, one day you’re a Yankees fan, the next day, Red Sox.”

WASP-12b is a gas giant, so its carbon-rich creations swirl within oceans of dense atmosphere. But what about terrestrial (i.e., rocky) carbon planets? Now it gets mighty interesting.

“If something like this had happened on Earth when it was formed,” Kuchner says, “your expensive engagement ring would be made of glass, which would be rare, because the atmosphere would be made of smog and the mountains would all be made of diamonds.”

artist concept of beta pic planetary system

Artist’s conception of the dust and gas disk surrounding the star Beta Pictoris. A giant planet may have already formed and terrestrial planets may be forming. The inset panels show two possible outcomes for mature terrestrial planets around Beta Pic. The top one is a water-rich planet similar to the Earth; the bottom one is a carbon-rich planet, with a smoggy, methane-rich atmosphere similar to that of Titan, a moon of Saturn. A team led by Aki Roberge of NASA’s Goddard Space Flight Center first presented the observation in the June 8, 2006, issue of Nature. Credit: NASA/FUSE/Lynette Cook

Kuchner says he thought initially carbon planets would probably be found in exotic stellar environs, like planetary systems whirling around pulsars or white dwarf stars. “But WASP 12 seems to be a pretty normal star, similar to the sun. If it could happen there, it could have happened here. And now that we know WASP-12b is a carbon planet. I bet we’ll start finding others.”

Well, that sounds familiar. In the early days of exoplanet discovery, we found “hot Jupiters,” gas giant planets orbiting shockingly close to their host stars. They seemed exotic until we started finding them all over the place. Now it’s “another day, another hot Jupiter.”

So perhaps carbon-rich planets won’t seem so strange someday, too. Case in point: a star called Beta Pictoris. Kuchner says Beta Pic is “mostly quite similar to the sun, but which has a planetary system and a disk around it that’s carbon rich. Not just a little carbon rich. It has nine times as much carbon as oxygen.  That’s even more carbon-rich than WASP-12b.”

We can only imagine what a planet might look like in such a carbon-mad place. We may never know, but it’s fun to wonder. The WASP-12b discovery gives us permission. “People sort of didn’t take the carbon planets idea seriously at first,” Kuchner says, “but this changes things.”

image of beta pic dust diskRIGHT:  This image of the circumstellar disk around Beta Pictoris shows (in false colors) the light reflected by dust around the young star at infrared wavelengths. The Beta Pic disk is very likely an infant solar system in the process of forming terrestrial planets. Credit: Jean-Luc Beuzit, et al. Grenoble Observatory, European Southern Observatory

OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.


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The birth, life, and death of alien planets: Goddard exoplanet scientists give you an update on what we (think) we know

December 6, 2010 5 comments

exoplanet sun panorama

The official count of candidate planets around other stars recently hit a whopping 500. But when the first extrasolar planets — often called exoplanets — were discovered, many scientists weren’t sure if they should believe their own data. The first confirmed exoplanets were found around a stellar corpse called a pulsar, born of a supernova explosion of a star. And we also found lots of so-called hot Jupiters, huge steaming gasballs orbiting many times closer to their host stars than Mercury orbits the sun.

365 days of astronomy logoHow do exoplanets come to exist? How do they evolve over billions of years? And how do they die? If you’re curious and have 10 minutes, listen to my podcast, The Birth, Life, and Death of Alien Planets, on “365 Days of Astronomy.” (It’s a daily podcast produced by the International Year of Astronomy 2009.) You can also just download the (11 Mb) .mp3 file here and listen to it on your iPod or other media player. This blog post is adapted from the podcast transcript, if you prefer to read rather than listen to the 10-minute broadcast

The race is still on to discover more planets, and scores are promised thanks to missions like the Kepler space observatory. Meanwhile, down here on earth, exoplanets scientists are scratching their heads, mining their data, and tweaking their theoretical models to try and make sense of the diversity of alien worlds we have already found.

Here at NASA’s Goddard Space Flight Center, where I work as a science writer, we’ve got a whole group of scientists obsessed with exoplanets. They took me on a whirlwind tour of the birth, life, and death of planetary systems. It all starts with a collapsing cloud of gas that forms an infant stars surrounded by a spinning disk of gas and dust — the stuff of which planets are made. A protoplanetary disk.

JENNIFER WISEMAN: Young protostars are buried in a large envelope of dense gas, kind of flattened like a fluffy pancake, but it can extend out to thousands of astronomical units, the distance from the Sun to the Earth.”

DANIEL PENDICK: That’s Jennifer Wiseman. She studies star birth and is the new senior project scientist for the Hubble Space Telescope. She’s also the chief of Goddard’s ExoPlanets and Stellar Astrophysics Laboratory, which is home to many of the exoplanet researchers here at Goddard.

WISEMAN: You have this puffy but dense sort of pancake of gas, swirling around, and in the interior part of this, material is being gravitationally sucked into a tighter accretion disk that’s right around this young forming star.

PENDICK: OK, so far so good. We’ve got an accretion disk, which is where planets come from. What happens next? I asked Hannah Jang-Condell, a post-doctoral researcher at Goddard and the University of Maryland. She’s also a member of the Goddard Circumstellar Disks Group, about a dozen scientists here active in exoplanet research.

JANG-CONDELL: So basically you’ve got a star. It’s not burning hydrogen yet. You’ve got this disk of gas and dust surrounding it. And planets are starting to form in this disk.

PENDICK: Hold on — did she say dust? As in those fluffy dust bunnies that inhabit the underside of my couch? Not exactly. When astronomers say dust, they mean tiny bits of solid stuff, like minerals and ices, floating around in space. The dust grains are on the scale of a micron—a millionth of a meter—in diameter.

JANG-CONDELL: It’s assumed that as you build these things up from the micron size to the centimeter size, that things stay fluffy. So sort of loosely bound aggregates. So they are a lot like dust bunnies at that stage.

PENDICK: So much for interstellar dust bunnies. Now, back to the planet building stage of our story.

JANG-CONDELL: So there’s two main scenarios for the way planets form. There is the core accretion scenario. So you start out with dust particles and they collide and coagulate and become larger and larger bodies. When it gets about 10 to 20 times Earth’s mass it’s able to accrete gas, and then the gas will stay on it. From that point it can accrete gas and become a gas giant planet like Jupiter.

The alternative scenario is called gravitational instability. In that case, you have a massive disk, and it’s cool enough and dense enough for it to start self-gravitating. So in other words, the disk will fragment, it will start to form a clump, the clump will become self gravitating, and eventually it will collapse to form a giant planet.

PENDICK: This all takes place in the space of a few million years — a cosmic blink of an eye. Gas giants have to form before all the gas in the system has either accreted onto the star or is blown away by the star’s radiation.

Once the gas goes away, the infant planetary system evolves into something called a debris disk. As Goddard exoplanet researcher Aki Roberge explains, the planet-building process continues in debris disks, creating larger and larger bodies called planetesimals. In today’s solar system, planetesimals are known as asteroids and comets.

AKI ROBERGE: They start colliding and sticking. Roughly speaking, it’s just hit-stick-hit-stick, get bigger and bigger and bigger.

PENDICK: Sometimes the collisions are not so sticky. The planetesimals smash together and generate lots of smaller debris particles. In fact, huge dusty disks were discovered around other stars for the first time in the 1980s. Astronomers dubbed them ‘debris disks.’

ROBERGE: Over the years, there’s been lots of pieces of evidence collected that these debris disks, they really are young planetary systems. So they are like young, dense versions of our own Kuiper and asteroid belts, and our own solar system probably went through a phase very much like it, a debris phase, when it was young.

So any giant planets that would form in the system have already formed because there is no gas left to form any giant planets. And some planetary embryos, maybe Mars sized bodies, are there already. So what’s happening is the late stage of terrestrial planet formation. So you are building up from Mars to real Earths.

PENDICK: Terrestrial planets can have violent births, as embryonic planets up to the size of Mars slam into others and build up larger planets. Also at this time, water rich comets may stream in and collide with the young terrestrial planets. This provides the raw material for oceans and atmospheres.

Theory tells us these events must be happening in the dusty disks astronomers study. But we don’t see any of this directly.

ROBERGE: All you can really see, ironically enough, is the very smallest portion. So what you see is the dust, tiny, tiny little dust [grains.] This is the dust that’s produced when two asteroids crash together and break up, or the dust that’s in a comet’s coma that’s being expelled as they evaporate. So actually we see the indirect signs. We can see the tiniest material but we know it has to be coming from bigger things.

PENDICK: At some point, things do settle down a bit. But even in a mature planetary system, the action is far from over. Planets continue to migrate in their orbits, or even be ejected from the system in hair-raising close encounters. And if a planet orbits close enough to its star — even closer than Mercury orbits the sun — it could spiral inward and be consumed. In short, entire planets disappear from planetary systems. Goddard exoplanet researcher Brian Jackson explains.

BRIAN JACKSON: Once you get that close, tides raised on the host star and tides raised on the planet can affect the orbit of the planet. Because the rotation of the star is so much slower than the rate at which the planet is going around, the bulge tends to point a little bit behind the planet. And you can think about the gravitational interaction with that bulge always pointing behind the planet a little bit kind of yanks back on the planet and that can reduce the orbital distance between the host star and the planet.

Eventually its orbit will shrink enough that it will be destroyed. That can happen within a few billion years. So a lot of these close-in planets that we see aren’t going to last more than a few billion years.

PENDICK: And even planets farther out from the star can experience dramatic changes because of tidal forces.

JACKSON: If the planet’s orbit is non-circular, then what happens is the size of the tidal bulge when the planet is closest to its host star is bigger than when the planet is farther away. The shape of the planet will change as it goes around in its orbit. That change, that periodic flexing of the planet, dissipates energy inside of the planet. It can drive volcanism, which can cause outgassing and provide an atmosphere for the planet. And we see this sort of volcanism powered by tides in our own solar system, for example, Jupiter’s moon Io undergoes the same sort of tidal heating…and that drives the volcanoes that erupt on the surface of Io.

PENDICK: In fact, tidal flexing could hypothetically turn the surface of a rocky planet into a lava sea fuel massive supervolcanoes. Or it could cause just enough heating to maintain a warm and stable climate, as earthly plate tectonics does on our world.

We used to think that solar systems eventually settle down and become middle-aged and sedentary, with stable and predictable behavior. But this does not appear to be the case.

JACKSON: Among planetary systems, the rule seems to be that interactions can be very violent and dynamic and the orbits can evolve pretty dramatically over time.

PENDICK: Planetary systems can even come back from the dead after the most violent event nature has to offer — the supernova explosion of a star. Goddard post-doctoral scientist John Debes has studied these born-again planetary systems. In fact, the first planets ever discovered around other stars were found orbiting a pulsar — the superdense rotating remnant of a star that went supernova.

JOHN DEBES: What people think happened is that after the initial supernova explosion some of the material fell back into a disk, and that allowed these smaller planets to form. And the only reason we found them is because pulsars are amazingly precise clocks, and you could measure the timing of the pulses of the pulsar, and see that that would change due to the orbital wobble of these planets.

What’s great about that system, even though it’s the only one that’s been found, is it really shows the sort of basic process for forming a planet must be pretty easy to do, because if you can do it in the fallback disk of a supernova, you can do it just about anywhere if you have the right amount of material and the right conditions.

PENDICK: Hot Jupiters spiraling to their fiery doom… planets par boiled in molten lava… worlds born from the ashes of dying stars. It sure isn’t your grandfather’s solar system science anymore, with well-behaved old planets in their stately settled orbits. As telescopes give us even sharper views of alien worlds, it’s hard to predict what strange world await discovery.

Astronomer Carolyn Crow, also the center of the solar system.
OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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A peek at the behind-the-scenes movie magic that created 'Using colors to search for alien Earths'

November 3, 2010 1 comment

Astronomer Carolyn Crow, also the center of the solar system.

Carolyn Crow, UCLA graduate student and center of the solar system.

Someday, when we have space telescopes that can narrow in on the exceedingly weak light from incredibly distant planets around other stars, what will we do with those precious photons?

If you want to know, read the latest web feature and watch the video from NASA Goddard. I wrote the feature, “Using planet colors to search for alien Earths.”

I also had a chance to sit in on the studio work that produced the video featuring Carolyn Crow, a young scientist who led the research on planet colors. (She is currently a graduate student at UCLA.) As commonplace as green-screen technology is today, it’s movie magic that never fails to impress — especially when used as cleverly as it is in this video.

Producer/director Scott Wiessinger created a colorful digital landscape in which Crow strolled among the planets of our solar system in a modern version of Gulliver’s Travels. NASA/Goddard astrophysics writer Frank Reddy provided a concise and clear script.

Here is a behind-the-scenes peek at the movie magic.

looking stage left

Carolyn Crow stands ready to gesture at imaginary planets on Goddard TV’s green screen stage. To eliminate shadows and get the best results from the green screen process, the stage is brightly lit.

carolyn crow being filmed in front of a green screen

Carolyn after being inserted into a digital landscape with starry background and planet Earth.

And here is the final result:

OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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GJ 758 B: The planet that wasn't is probably a star that nearly isn't. And in the end it's all about the nature of scientific evidence and how we decide something is true

September 30, 2010 3 comments
image of GJ 758 made with mmt telescope

Thayne Currie and his colleagues created this image of GJ 758 using observations collected earlier this year with the 6.5-meter MMT telescope. The central speckled white region is the star. GJ 758 B lies below and slightly to the right of center.

Well, GJ 758 B, you were almost a planet. But it sure looks like you aren’t anymore, so be big grown-up brown dwarf and get over it, ok?

Last year, it sure seemed like the object dubbed GJ 758 B could be a giant gaseous planet circling a star a lot like our own. It sparked more than a few headlines in the science press, including this one: “First Cool Exoplanet Around Sun-like Star Imaged”

Although the headline seemed to confer planethood on GJ 758 B, the writer included this caveat in the text:

“With an estimated mass of 10 – 40 times Jupiter’s mass, GJ 758 B is either a giant planet or a lightweight brown dwarf.”

A lightweight brown dwarf, y’understand, is a dim, cool ball of gas too big to be a planet but too small to ignite fusion of hydrogen into helium in its core so it can radiate lots of energy and thus claim star status.

Brown dwarfs are the almost-but-not-quites of the stellar zoo. Sure, they can fuse a slightly heavier form of hydrogen, deuterium. But that doesn’t make it a full-fledged star. Brown dwarfs are, in astro-speak, “sub-stellar.”

Recently a team led by Goddard’s Thayne Currie reported new information about GJ 758 B. Here is his one-sentence summary of his research paper, published September 13 in Astrophysical Journal Letters:

“We confirm that GJ 758b is the coldest, faintest object that has ever been imaged around a star like the sun, but show that it is probably not a planet, as was originally claimed by some scientists.”

In 2009, a different team reported a preliminary mass estimate for GJ 758 B of “10 to 40” times the mass of Jupiter. Exoplanet people use such “Jupiter masses” as a convenient way to talk about the heft of big planets. Read all the details in a Centauri Dreams post from last year.

click to make me bigger!

The Subaru Telescope captured this image of the sunlike star GJ 758 in August 2009. The light of the star is blocked out, leaving the near-infrared glow of two other objects. New observations suggest GJ 758 B is not a gas giant planet, as previously suspected. There is weak evidence that another object, called GJ 758 C, also orbits the star.

When someone spots a really big ball of gas orbiting another star, mass is the key issue. When does a planet get too big for itself and then have to be called something else?

Currie and his colleagues used the 6.5-meter MMT telescope earlier this year to observe GJ 758 B and get better measurements of its temperature and luminosity (the rate at which the star radiates light). And that allowed them to come up with a better estimate for the object’s mass.

The answer: GJ 758 B most likely exceeds the 13-Jupiter-mass threshold at which sunlike balls of gas start fusing deuterium and are no longer considered planets.

If it all still sounds uncertain, it is. Or should I say: Of course it is.

Reporters and bloggers prefer clear, simple answers. But that is not what science usually provides. Science builds up better and better evidence for a particular interpretation of evidence, called a hypothesis.

I asked Currie how sure he was that GJ 758 B is not a planet. He said:

“Well, as with all things in science, we don’t have ‘proof.’ However, a couple of highly improbable things would have to conspire together in order to make its mass be consistent with a planet.”

One of those improbables is that the star would have to be much younger — less than a billion years old — than all the signs point to.

For instance, there is a sign called chromospheric activity, which is associated with the amount of heating that occurs above the visible surface of a star. Chromospheric activity decreases with age. And the degree of it we see from the star GJ 758 is similar to that of our own sun — our middle-aged, 4.6-billion year-old sun. Hold that thought for a moment.

Theories of planet formation say that if GJ 758 B is less than 13 Jupiter masses, and therefore a planet, it’s home star should be about a billion years old. But it would be very strange indeed for a star that young to have the relatively low level of chromospheric activity that we see.

Get it? Given all the information we have, it’s more likely that GJ 758 B is a brown dwarf.

So in the end, whether GJ 758 B is a planet depends on other things being correct or incorrect, including theoretical models for how planets form and how old certain types of stars are based on things we can measure, like chromospheric activity.

If you unpack the whole GJ 758 B discussion/debate, it actually turns out to be about something much bigger: What constitutes evidence, and how do we come to trust a particular interpretation of it?

Well, that sure sounds like the essence of the debate over global climate change. And the controversy over “intelligent design” vs. Darwinian evolution. And part of the reason why millions of middle-aged women were given estrogen replacement therapy only to find out later that it was associated with an unexpectedly large risk for cancer and heart disease.

Who knew a story about a little star called GJ 758 would actually turn out to be a lesson in the philosophy of science?

OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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Bodies in motion: a computer modeling trick developed at Goddard allows us to simulate what our solar system looks like to aliens

September 23, 2010 1 comment

A few years ago, a University of Maryland graduate student, Christopher Stark, crossed paths with NASA astrophysicist Marc Kuchner. “He landed in my office and asked me if I had any projects,” Kuchner recalls.

Stark needed to do some interesting and original science so he could become a professional scientist instead of a professional student; Kuchner needed help with his interesting and original research on how planets sculpt the disks of dust and gas in alien star systems, creating features like rings, gaps, and clumps.

And maybe, just maybe, by imaging those rings, gaps, and clumps in disks of dust around alien star systems, we might be able to discover planets. In other words, we might find planets by spotting their gravitational pull on their surroundings, as opposed to taking a picture of the actual planets, which is a rare and delicate trick.

New model

Fast forward to summer 2010. Stark finishes his PhD thesis on computer modeling of dust disks around alien stars, gets a sweet job at Carnegie Institution for Science in Washington, D.C., and is the lead author on a paper describing aforementioned interesting and original science in the September 7, 2010, Astronomical Journal. Life is good!

Read the Goddard Space Flight Center press release and video for the science details. Stark and Kuchner basically simulated the dust in our own solar system and showed what it would look like to alien astronomers observing from afar. (Hint: they can see a ring-shaped collection of dust with a gap due to the influence of Neptune.)

Here, let’s talk about how Stark and Kuchner simulated dusty solar systems in the supercomputer down the hall from me.


click to make me bigger!

The “debris disks” around stars contain an unimaginable number of tiny grains of dust — “dust” being tiny clots of crusty minerals and frozen vapors. Fluffy interplanetary dust bunnies, really.

As planets orbit, their gravity can induce rings and clumps in the dust. And because warm interplanetary dust radiates infrared energy, telescopes trillions of miles away can actually SEE the rings and clumps even though they can’t see the planets creating them.

Kuchner and Stark decided to build a more realistic computer simulation of dusty disks with planets. It could prove a pretty handy tool for spotting planets someday.

The problem: too many dust bunnies! Getting a computer to track the movements and interactions of so many bits of stuff is, well, practically impossible.

Ever heard of the “three body problem”? For physicists of olde like Sir Isaac Newton, calculating the motions of three gravitating bodies in free space was enough to induce cardiac arrest. Dauntingly, terrifyingly, slide-rule-breakingly hard.

“How,” Kuchner asks, “do you figure out the answer without having to figure out a billion billion billion collisions?”

Stalking dust bunnies

Tracking a billion billion billion dust bunnies is not even worth considering, even with the formidable computing resources down the hall from me at Goddard, that being the Discover supercomputer.

But Stark and Kuchner found a way. They call it the collisional grooming algorithm.

An algorithm is a precise set of mathematical rules that describes how to solve a problem. Stark and Kuchner used it to simulate 75,000 virtual dust particles and track their motions and number in response to grain-grain collisions and the gravitational tug of planets.

But what about all the other dust bunnies, the billion-billion-billion?

“We allow each single integrated particle to represent many dust grains,” Stark explains. “We scale the number of dust grains up and down to control how much dust is in the disk, even though we only actually integrate 75,000 particles.”

But let nobody leave the room thinking that approximating the behavior of 10 billion billion billion dust bunnies is easy.

At Goddard, we have a supercomputer called Discover. The thingies that do the actual data processing in a computer are called processors, and Discover presently has about 15,000 of them. That’s the number of processors in 7,500 MacBook Pro laptops like the one I used to write this blog post. Which is to say, my laptop packs an Intel Core Duo, or two processors, whereas the Discover supercomputer packs about 15,000 processors. Soon, Discover will double in capacity to nearly 30,000 processors.

To run Stark and Kuchner’s interplanetary dust bunny simulation required about 3,000 processors — the equivalent of 1,500 MacBook Pro’s — running for 24 hours!

OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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