Tag Archives: JPL

Chandrayaan-1: the Lost and Found Lunar Orbiter

This is pretty cool. ¬†ūüėČ

On October 22, 2008, India joined the elite group of nations which have successfully sent spacecraft to orbit the Moon. ¬†The mission was successful, conducting joint operations with NASA’s Lunar Reconnaissance Orbiter and LCROSS impactor, deploying an impactor of its own to help search for lunar ice (and making India only the fourth country to place its flag upon the Moon), and providing the first definitive proof of water ice in the lunar soil. ¬†The mission was cut short, however, when the spacecraft abruptly stopped responding to ground commands on August 29, 2009. ¬†The cause of the failure was never determined, but it had been experiencing issues in several systems, including the star tracker that keeps its antenna aligned with Earth.

Like other deep space spacecraft, the moment it stopped transmitting it became impossible to track from Earth — the Moon is much too far away to track such small objects (in Chandrayaan-1’s case, about 1.5 meters by 1.5 meters) by radar.

Or is it?

As international governmental and private space programs grow at an astonishing rate, it has become clear that space traffic will increasingly become a problem not just in Low Earth Orbit (LEO) and in the immensely valuable Geostationary Earth Orbit (GEO, the province of most communications satellites) but in deep space as well. ¬†The recent move of the MAVEN spacecraft to dodge Mars’ innermost moon, Phobos, also underscores the hazards. ¬†So JPL conducted a study to see whether lunar spacecraft actually¬†could be tracked from Earth. And guess what — they can!

JPL’s first target was LRO, because it’s an active spacecraft and therefore its real position is known with exquisite precision. ¬†Having located it with ground-based radar, the team moved on to something trickier: the Chandrayaan-1 spacecraft. ¬†Lunar spacecraft are difficult, because the Moon is so lumpy that a) dead spacecraft don’t stay long unless their orbits are fairly high, and b) orbits can be difficult to predict over long timescales. ¬†Nevertheless, they found it. ¬†Chandrayaan-1 is dead, but not gone, and certainly not forgotten.

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Pan, the Space Ravioli

Seriously, that’s what Saturn’s moon Pan looks¬†

Cassini has just made the closest ever pass to Pan, one of Saturn’s shepherd moons. ¬†It orbits within (and basically creates) the Encke Gap in Saturn’s rings. ¬†The wide flat band of material around its equator is material accreted from the rings themselves. ¬†The best part, though, is that the Cassini imaging team at JPL put together this neat animated GIF collecting all of the raw images from this particular imaging sequence, and its glorious:

 

It’s bittersweet, knowing that these close orbits are dooming Cassini to eventually fall into the giant planet, but we’d never get these incredible images otherwise, images of the greatest natural lab we’ve ever found for studying the way a planetary system can form.

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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):

pia21428_-_trappist-1_comparison_to_solar_system_and_jovian_moons

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Daphnis, the ring-sculptor

Strictly speaking, Daphnis is one of many ring-sculptors — the shepherd moons that maintain some of the notable visual features of the rings of Saturn. ¬†In the case of Daphnis, that’s the Keeler Gap, a narrow gap carved out the A ring by the gentle gravitational tug of war between Saturn and the tiny moon.

Daphnis was actually discovered by the Cassini probe in 2005, but its existence was suspected long before, when the Keeler Gap was itself discovered in images taken by the twin Voyager probes. ¬†Voyager had already discovered the moons Prometheus and Pandora, which the Voyager team dubbed “shepherd moons” for the way their push and tug confined a group of particles to¬†the very narrow F-ring. ¬†So it was surmised that the other gaps would turn out to have moons creating them as well.¬†Mimas seems to be responsible, at least in part, for both the Cassini Division and the Huygens Gap, and of course Prometheus and Pandora constrain the F ring. ¬†Pan, discovered in 1990 from old Voyager data, is likely responsible for the Encke Gap. ¬†And Daphnis is the sculptor of the Keeler Gap.

Or, at least, the main sculptor. ¬†Saturn’s rings are very complex, and serve as a fascinating natural laboratory for studying gravitational interactions, and particularly the sort hypothesized to have created the solar system as we know it. ¬†And Daphnis, like other shepherd moons, does not orbit perfectly neatly. ¬†Its orbit is slightly inclined relative to the ringplane, and slightly elliptical as well. ¬†Thus, it doesn’t produce a nice tidy circle, but carves out waves as it passes — waves both ahead and behind, and, as this recent Cassini image shows, sometimes it pulls off delicate tendrils of ring particles (look verrrrry closely, or just click to enlarge – you’ll see a thin wisp of material echoing the shape of the nearby wave in the ring):

That’s the closest image ever taken of Daphnis, a tiny moon roughly the same size as Mount Everest. ¬†It appears to have striations running down its length, probably the result of accumulated ring particles — sometimes, even a tiny moon like this will manage to capture something and pull it down. ¬†But if you want a more dramatic image of this effect, you will have to look at Daphnis near Saturn’s equinox, when the shadows are at their longest. ¬†Then you can see what is hidden in this image: the waves aren’t just flat features. ¬†They stand surprisingly tall.

By studying this process, scientists hope to better understand planetary formation. ¬†Indeed, they’ve even found a few spots in Saturn’s rings where it appears that moonlets may be in the process of forming, clumping together at random until eventually one clump reaches a critical mass and begins to dominate the particles around it, gradually growing until it exhausts its immediate surroundings, carving out another gap. ¬†Daphis itself shows signs that it may be accumulating material. ¬†Saturn’s rings are an astonishingly and fascinatingly dynamic place.

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NASA announces two new deep space missions: Psyche and Lucy!

So here’s something else to look forward to: today NASA announced two missions to asteroids. ¬†Psyche will visit the asteroid 16 Psyche,¬†a gigantic¬†nickel-iron asteroid so big that astronomers have speculated it could be the core of a destroyed planet. ¬†Lucy, meanwhile, will visit¬†half a dozen Trojans — asteroids co-orbital with Jupiter, swept up into Jupiter’s enormous Lagrange points. ¬†Four of Lucy’s targets are around¬†the Sun-Jupiter L4 point, and the other two are at the L5 point. ¬†(“Points” is a little misleading here, by the way. ¬†There’s actually a vast zone in which lagrangian companions might be found.)

Both are relatively fast and inexpensive Discovery class missions. ¬†The Discovery class missions have an impressive legacy despite their austere nature — NEAR, Mars Pathfinder/Sojourner, Lunar Prospector, Stardust/NeXT, Genesis (which had an unfortunate failure of the sample return capsule), CONTOUR (lost due to an engine failure), MESSENGER, Deep Impact/EPOXI, Dawn, Kepler, GRAIL, and InSight. ¬†These missions also share heritage with New Horizons, as they are slated to use newer versions of some of the instruments first flown on that mission.

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Curiosity’s drill is down

The Mars Science Laboratory “Curiosity” is an amazing vehicle in an exceptionally hostile environment, and it seems it is having some issues with its drill. ¬†The drill itself is working fine, but the motor that extends the drill bit forward to touch the rock face is not cooperating. ¬†As a consequence, Curiosity is on non-drilling duties while the JPL team analyzes the problem and decides what to try next. ¬†Fortunately, it has a wealth of other instrumentation, so Curiosity has been far from idle. ¬†Here’s one of the pictures it took while on its “drilling hiatus”:

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Cassini’s ring dives have begun

With its last flyby of the giant moon Titan, Cassini grabbed a gravity assist and slipped into an orbit that ventures closer to Saturn than any previous orbit.¬† This is the final phase of the Cassini mission, focusing on Saturn’s rings and the enormous gas giant itself.¬† This final mission begins with 22 orbits dipping almost to the F ring.¬† These orbits are much smaller than previous orbits, so they go much more quickly; the orbit will be adjusted again in April to set up another 22 orbits, these dipping inside the rings.¬† Those orbits will wrap up in September of 2017, when Cassini will plunge into Saturn itself.¬† It’s hard to believe it, but by that time, Cassini will have been in space for nearly 20 years.

Some of the first images from Cassini’s latest, closest periapsis (perikrone?) have been released.¬† Here’s the mysterious Hexagon from Saturn’s north polar region:

And here’s one of many raw ring images sent back, this one acquired December 5:

Stay tuned for spectacular new images as Cassini moves ever closer!

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