Tag Archives: exoplanets

The seven rocky worlds of TRAPPIST-1

NASA had a big announcement today: the dwarf star TRAPPIST-1 has at least seven terrestrial planets, and at least three of them are in the star’s “goldilocks zone”, where liquid water could exist on the surface (assuming sufficient atmospheric pressure).

TRAPPIST-1 got its name from a Belgian telescope called the Transiting Planets and Planetesimals Small Telescope, situated at La Silla Observatory in Chile’s Atacama Desert.  TRAPPIST found that the star (catalogue number 2MASS J23062928-0502285) had at least three exoplanets orbiting it by observing the star’s lightcurve change as the planets transited.

Subsequently, NASA’s Spitzer Space Telescope was called in to confirm the discovery, in a marathon 500-hour focused study of the TRAPPIST-1 system.  And it did!  Today, NASA announced that not only are the three worlds real, there are at least four more.  And at least three but possibly all of them are in the habitable zone.  This is the largest collection of terrestrial worlds ever found.  Since they orbit quite near their dim parent, astronomers were able to calculate their densities, and they’re pretty close in size to Earth — some are actually smaller.

The Hubble Space Telescope is now being called in to study the planets in more detail, and hopefully to determine whether or not any of them has a substantial atmosphere, preferably one with an unusual concentration of hydrogen, which would imply water vapor.  So far, it hasn’t found evidence of an atmosphere (and has largely ruled out the kind of atmosphere we’re all hoping for on TRAPPIST-1b and TRAPPIST-1c), but they’re still looking, and the search is expected to continue into the James Webb Space Telescope.  The hobbled Kepler Space Telescope (now “K2”) has also been studying this system.

Here’s an artist’s concept, to show you the relative sizes (note that color is completely imaginary at this point):



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The exquisite poetry of exoplanets

With all that’s been going on, sometimes it’s nice to remember how beautiful the universe is. And just to prove that, here’s a video of the four large planets of the star HR 8799, gently revolving around it.  They’re big and distant — all four planets are estimated to be larger than Jupiter, and the closest-in one has a forty-year orbit.  (The most distant takes ten times longer to orbit the star.)  And there’s an extra bit of beauty here: the planets are in a resonance of 1:2:4:8.

This isn’t a real movie, in the sense of being tape-recorded.  Instead, it was constructed from eight images taken with the Keck telescope in Hawaii since 2009, with the paths of the worlds interpolated between frames to create smooth motion.  It’s not the first direct image of exoplanets, nor the first video showing their motion, but it is decidedly beautiful.


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Space is dangerous: CoRoT is the latest casualty

Space is dangerous.  With launch hazards, the impossibility of repair, the concern of design errors undetected until the spacecraft a thousand miles away and forever unreachable, draining batteries and degrading solar arrays, growing tin whiskers and diminishing fuel reserves, micrometeoroids and an increasing abundance of space debris, it’s amazing that mission-ending accidents don’t happen more often.

And there’s one more hazard I didn’t mention: radiation.

Computers don’t get cancer or develop radiation sickness, but charged particles can flip bits in a circuit or even saturate a circuit so severely that it melts through in one spot and causes a short.  It’s a serious problem that contributes heavily to the cost of a spacecraft in shielding, careful circuit protection (especially around solar arrays, which are exceptionally good at grabbing charged particles and feeding them right into the circuitry), and massive error correction in both hardware and software — since corrupted data can be a very big deal, if the corruption is in a computer instruction.  Even the signals received from the ground can become corrupted in this way, so it’s a huge focus of spacecraft design.

And sometimes all that engineering effort is not enough.  There is no way to complete protect all of the computer circuits, all of the instructions, all of the data storage, all of the communications, so instead you protect as best as is practical and then you cross your fingers.  The current solar maximum has been cooperative as far as that goes, with space weather much more benign than it normally is during the solar peak.  But “more benign” is not the same as “mostly harmless”.  And now the French Convection, Rotation and Planetary Transits (CoRoT) space telescope has been hit.

CoRoT is not completely dead, but no data has been received from its main instrument, a 27 cm telescope and camera designed to patiently scan the sky in hopes of capturing a planetary transit around a distant star.  It’s been functioning great since its launch in 2006 (not bad for a three year primary mission), discovering dozens of planets and a great many basic science contributions to astrophysics, but now its mission is over.  Controllers on the ground will perform a series of engineering experiments with it, and then will safe it, which will mostly consist of safely discharging its batteries and feathering the solar arrays so it is less likely to explode when uncontrolled.  It will eventually fall out of orbit.

Good work, CoRoT.  Sad to see you go, but you’ve done well.  Bonne nuit.

CNES: CoRoT mission page


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