steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Cassini spots mini Nile River on Saturn moon

Cassini's radar imaging of Titan has spotted evidence for a 400 km long river on Titan, with its mouth in a lake. Lakes and rivers on Titan are made of liquid methane/ethane, not water, which is frozen rock-like at Titan's temperatures. The riverbed-shaped structure is apparently full of liquid, not a dry empty riverbed, because it appears dark to the radar, indicating that it has a smooth surface.

I'm not sure why it's compared specifically to the Nile river.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
A fifth moon of Pluto has been discovered.

Here is a Hubble Space Telescope press release.

And here is an article from Sky and Telescope.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Cassini has found evidence that Titan has liquid water beneath its surface. Saturn causes tidal distortions in Titan; if Titan were solid all the way through, we'd expect to see relatively small tidal distortions, but Cassini has instead found much larger ones, which suggests that part of its interior is liquid and thus more easily distorted.

Here are two articles on the topic, one from NASA and one from ESA.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
A couple weeks ago, there was news about a new analysis of what's going on under Europa's surface.

We've been pretty sure for a while that somewhere under Europa's surface, there's an ocean. But a big question has been how far under the surface that ocean is. Some facts seemed to suggest that it was quite close to the surface - patches of 'chaos terrain' that looked like ice had broken up, jostled around, and refrozen back together. But other facts implied that the icy shell outside the ocean must be quite thick. It hasn't been at all clear how these apparently conflicting pieces of evidence should be resolved. The new work proposes a model where the icy shell is quite thick, but within the icy shell there are melt pockets - like underground lakes - that cause chaos terrain above them.

As usual, Emily Lakdawalla has a good write-up of it.

More links:
Sky and Telescope: Europa's Subsurface Lakes
University of Texas at Austin: Scientists Find Evidence for “Great Lake” on Europa and Potential New Habitat for Life
The original article in Nature, for those who have subscription access.
A NASA press briefing

On November 6th, 2011, Cassini did a flyby of Enceladus that was devoted to taking synthetic aperture radar (SAR) imaging. This is pretty unusual; normally, Cassini only uses the SAR imaging on Titan, in order to peer through Titan's haze. Since other moons don't have significant atmospheres, SAR isn't important to be able to see their surfaces.

The Cassini website has just released a news item about the flyby; it has a link to a video that shows the radar swathe overlaid upon an ordinary image of the surface, and then shows close-ups of two particular regions of the swathe.

Again, Emily Lakdawalla has a good post about the topic. She points out that the purpose of this is actually more to help us understand Titan than to help us understand Enceladus; SAR is often hard to interpret, and by using it on a surface where we can check what we're finding against visible-light (and ultraviolet/infrared) imaging, we can get a better idea of what SAR images of Titan mean.

EDIT Dec. 2, 2011: Apparently, Cassini has in fact taken SAR images of Enceladus before, as well as of Rhea and Iapetus; however, it seems that the previous images were much lower resolution. Discussion here on the Unmanned Spaceflight forum, with links to images.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Tiny, Gentle Pluto May In Fact Be A Killer

A bit of an overdramatic headline, but the article's got interesting stuff in it. The core idea is that the New Horizons spacecraft is on the way to the Pluto system, scheduled to arrive in 2015; when the project was first designed, Pluto was only known to have one moon, the rather large Charon, but since then, 3 smaller moons have been discovered - two that were first suspected in 2005 and confirmed in 2006, and one that was discovered in 2011. And there are suspicions that there may be more small moons; partly this is a matter of "well, if there were three hiding until recently, maybe there are more that are still hiding", but there's a more concrete aspect: there were actually two specific satellite candidates that were found, but more observation is needed in order to figure out if they're actually satellites or not. In addition, there's a possibility that impacts onto these moons may create rings around Pluto. The more moons and rings there are around Pluto, the more risk there is that New Horizons will smash into something and be damaged or destroyed when it gets to the Pluto system.

I'd heard before about the concerns for New Horizons about Pluto having more moons and rings. What was new to me in this article, and particularly interesting, was that there are specific identified candidates for further moons, not just a general sense that there could be more moons.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Extreme Ballooning -- on Titan

On efforts to develop a hot air balloon for a mission to Titan; this has an advantage over a lander that a balloon can move around and give you a view of a variety of different places. A major challenge for developing a balloon for Titan is that it's so very cold.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
On Friday there were three press releases:
Number one: Subtly Shaded Map of Moon Reveals Titanium Treasure Troves. Certain parts of the moon have surprisingly large amounts of titanium. Maps of the moon in visible and ultraviolet light show which parts of the moon are high in titanium. We don't really understand why the moon has as much titanium as it does, but it does give us some clues about the history of the moon. These visible and ultraviolet light also show some interesting things about space weathering.

Number two: The cause of asteroid Scheila’s outburst. In 2010, the asteroid Scheila started showing comet-like features, including a tail. Material presented at the conference provides evidence that this was caused by an impact from a much smaller asteroid (Scheila is about 110 kilometres in diameter; the impactor is calculated to have been between 60 and 180 metres in diameter, so about a thousandth of Scheila's diameter.)

Number three: Almahata Sitta meteorites come from triple asteroid mash-up. On Oct. 7, 2008, three years to the day before the date of the press release, for the very first time an asteroid which had been detected in space and predicted to hit Earth actually did so. It landed in the Nubian Desert in Sudan, and more than 600 fragments have been retrieved. They're named Almahata Sitta. The varying composition of the fragments suggests that they belonged to a parent body that was created by relatively low-speed collisions between asteroids of different types.

And here's Emily Lakdawalla's post on Day 5 of the conference. Some of the things she talks about: the great storm on Saturn; Mars's moon Phobos is probably a rubble pile; there's good evidence that the grooves on Phobos are caused by stuff ejected by impacts on Mars; a more precise calculation than previously of the mass (and thus density) of the asteroid Lutetia; the asteroids Lutetia and Steins both have more recent large craters than we'd predict, which suggests that we may be underestimating the number of small asteroids.

Now for other bits and pieces and news stories written up by people besides me, from any part of the conference, not just the last day:

Emily Lakdawalla's notes on NASA's Planetary Night, "in which representatives from NASA's Science Mission Directorate speak to the people whose missions and research they fund about their accomplishments and the political and funding climate for the coming years". Most of the news is pretty discouraging, but there's one bright bit: that the production of Plutonium-238 is going to be restarted, so there will be a reliable power source for missions that can't use solar power.

A Whole New World at the Edge of the Solar System. About Kuiper Belt Objects, what we can learn from light curves, what they say about Haumea, what a contact binary is, and, in culmination, how the light curve of a certain Kuiper Belt Object shows that it's a contact binary, and why changes in that light curve over the past few years give an indication that such contact binaries may be common among Kuiper Belt Objects.

The Revelations of Planets' Shadows. About what we've learnt about Makemake and Quaoar from them occulting stars.

Did Earth's oceans come from comets? The water in previously observed comets has about twice as much deuterium (hydrogen with a proton and a neutron rather than just a proton) as Earth's water does. This was a problem for accounts of the origin of Earth's water that said it came from comets. But recent observations of comet Hartley 2 show that it has almost exactly the same amount of deuterium as Earth's water. It was formed in a different part of the solar system from the comets that were found to have more deuterium than Earth's water, and this probably explains why it's different from them.

When Minor Planets Ceres and Vesta Rock Earth Into Chaos. The two largest asteroids, Ceres (which is a dwarf planet as well as an asteroid) and Vesta, gravitationally affect each other; they also gravitationally affect earth, so that we can't reliably predict Earth's orbit farther into the future than about 60 million years; we also can't reconstruct the details of Earth's orbit farther back than about 60 million years.

Did Mercury and Uranus Have a Rough Youth After All? About the early history of Mercury and Uranus, and how many major impacts they received; for Mercury, it's about the question of how it got its present density while retaining relatively volatile elements like sulfur and potassium, while for Uranus it's about the idea that several major impacts gave it its present large tilt.

Pea shooter theory aims to build solar system. About a new tentative hypothesis about how the planets of the solar system formed - that rather than forming in about the regions where we now find them, they all formed initially at roughly Earth's distance (well, at least the ones outwards of Earth) and made their way outwards to their present distances.

And finally, one thing I found on Twitter but not in the articles mentioned above. Again, don't take my extractions of stuff from Twitter too seriously.

Satellites of Mars
There was a talk arguing that Phobos and Deimos were created out of the debris from a large impact on Mars - the impact would have created a debris disc around Mars, which then accreted into Phobos and Deimos. This explains their orbits better than the idea that they're captured asteroids - their orbits are too circular and too much in the same plane to be captured asteroids. Mars's rotation rate also implies that Mars got a large impact, and there are several impact basins on Mars that are the right size to account for both the spin rate and the moon formation.

Twitter source:
[ profile] kat_volk
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Three press releases today:
Number one: ESA finds that Venus has an ozone layer too. It was already known that Mars as well as Earth has an ozone layer. They found Venus's by analyzing the spectra of stars seen through the very outer edge of Venus's atmosphere.

Number two: The Secrets of Asteroid Minerva and its Two Moons. Moons let scientists figure out Minerva's mass. They figured out its diameter from a combination of watching it occult a star, and infrared measurements, both of which pointed to a diameter of about 156 km. This lets them calculate its density - about 1.9 grams per cubic centimeter; based on the density of what they think it's made of, that indicates that it must have about 30% empty space in its interior.

Number three: Series of bumps sent Uranus into its sideways spin. This is about a new hypothesis, not a new discovery. The previous standard account for Uranus being tilted on its side was that a single large impact had changed its orientation. The problem with that explanation has always been that it didn't explain why its moons orbit it in similarly tilted orbits. New computer simulation results show that this can be explained if Uranus was hit before the moons formed, while it was still surrounded by a protoplanetary disc out of which the moons later formed, and if it was tilted by two or more impacts, rather than by a single one.

And what I got from Twitter. As before, don't put too much confidence in it; I could very well have misinterpreted things or expanded them wrongly.

I'm not sure how much of this is new, but: Venus has lightning, and like on Earth, some days have more lightning than others, depending on the weather. The lightning rate on Venus is probably comparable to that on earth, about 100 flashes a second worldwide, but that's hard to prove.

Venus's cloud tops are generally 72 km above the surface, except at the poles where they're only 65 km up.

Global climate models for Earth aren't working for trying to understand Venus, which indicates that they might not be working right for Earth either. To understand Earth's climate, we have to understand Venus too.

Saturn's moons
One of the puzzles about Saturn's moon Iapetus is why it has a ridge running around its equator. One hypothesis has been that it used to be spinning faster, which made it more oblate (i.e., bigger around at the equator than at the poles) due to centrifugal effects, but its rotation slowed, so gravity made it more spherical than oblate, but the rearrangement process from more oblate to less oblate created an equatorial ridge. The problem with that is how exactly the spin change could have worked to create that result. The proposal now presented is that if Iapetus once had a satellite of its own, that might make it possible to reduce Iapetus's spin enough to create the ridge. (I don't know how a satellite would help that, though.)

It was discovered over a year ago that Mimas has a weird Pac-Man-shaped temperature pattern; there's a relatively warm area that looks like a Pac-Man shape on images, and relatively cold area on the leading hemisphere that looks like the inside of Pac-Man's mouth. News: The cold part of the leading hemisphere - the area inside Pac-Man's mouth - is correlated with an area in the leading hemisphere that is dark in UV light. Also, as of September 2011, a similar anomaly seems to have been observed on Tethys. (I think this means both the temperature pattern and the correlation with a UV-dark leading hemisphere area have been observed on Tethys, but I'm not sure about the second half.) There's a hypothesis, which still sounds quite tentative, that it might be caused by being bombarded by electrons, which somehow (not clear from Twitter) increase the thermal inertia of the moon's material. (Also not entirely clear to me whether the electrons are bombarding the warmer area or the colder area.)

The outer irregular satellites of Saturn that Cassini observes are so faint that if you were sitting on Cassini, you couldn't see them with the naked eye.

Other stuff
Almost all near-earth asteroids smaller than 60 metres diameter rotate really fast - in less than 2 hours.

Dust from collisions between irregular satellites of Jupiter might have left 100 metres of dust on Callisto and 20-30 metres of dust on Ganymede.

It sounds as if there was some interesting stuff about Europa, but not that I could contextualize well enough to pick out relevant tweets and expand on their significance as needed.

Good news: Jim Green, the Director of Planetary Science for NASA, says that production of Plutonium-238 will be restarted, so there will be a reliable power source for outer solar system missions.

Twitter sources:
[ profile] DrFunkySpoon
[ profile] kat_volk
[ profile] gsinfinite
[ profile] elakdawalla
[ profile] jeanlucmargot
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
First, stuff written up by other people.

It looks like there's only one press release today, on MESSENGER at Mercury (related graphics here). Among other things, Mercury's magnetic field is weird - it's shifted north by about 20% of Mercury's radius, so the field is stronger in the northern hemisphere than in the southern hemisphere.

Emily Lakdawalla's daily summary is also all about MESSENGER's results at Mercury, and goes into some stuff that didn't make it into the press release, such as that Mercury seems to be made of darker stuff than the Moon, and that Mercury has a smaller range of heights between highest and lowest than the Moon or Mars. (Mercury: about 10 km; Moon: about 20 km; Mars: about 30 km).

Stuff from Twitter; again, take with many grains of salt, because I don't know what distortions I may have introduced.
Elaboration on the weird magnetic field: the magnetic field's axis is aligned with the rotational axis, to within 3 degrees; but the magnetic field itself is shifted north along that axis.
Mercury's crust is about 50-80 km thick at the equator, 20-40 km thick at the north pole.
Mercury's surface is low in titanium and iron, but has lots of sulfur.

The state of relaxation of craters in the northern hemisphere of Enceladus indicates that even heavily cratered parts of Enceladus (i.e., the parts where craters haven't been overrun by geological activity) indicates that even those regions have to have had a (relatively) high heat flux in the past.

Earth's Moon
Ancient craters and relatively recent craters have different size distributions. The size distribution of ancient craters looks like what you'd get if you took stuff indiscriminately from the main asteroid belt and smashed it into the Moon. The size distribution of more recent craters looks like the size distribution of near-earth objects, which are removed from the main asteroid belt by a process that's affected by size, the Yarkovsky effect.

Other stuff
Saturn's moon Aegaeon is really really elongated: 1.4 x 0.5 x 0.4 km.

Twitter sources:
[ profile] spacemandave
[ profile] DrFunkySpoon
[ profile] elakdawalla
[ profile] asrivkin
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Again, first more information presented by people who know more than I do:

Emily Lakdawalla's post on Day 2 includes:
- a bit about recent flyby data from the comets Hartley 2 and Tempel 1.
- size data on Makemake based on an occultation; also, results from infrared data indicate that Makemake has a surface with mixed really really bright and really really dark patches
- weird results from an occultation about Quaoar's size - it 'looked like someone had taken a bite out of it'
- a few things about Titan

Three official press releases of the day:
One on a discovery made using the Kepler spacecraft on the discovery of a star with three identified planets. The smallest has a mass of 6.9 times that of Earth, while the larger two have mass of 16-17 times that of Earth (i.e., about Neptune's mass). All three are much closer to their star than Mercury is to the sun.

A second on oddities of comet Hartley 2, including that it may be two former comets that got stuck together.

Third, and most exciting to me, is one about a global false-colour map of Titan using data from Cassini's Visual and Infrared Mapping Spectrometer (VIMS). This is really hard to do because of Titan's atmosphere, which is opaque to most wavelengths of light, and even with the wavelengths that can penetrate it, there are still atmospheric effects, e.g. from clouds and mist.

And now for what I've managed to extract from Twitter. As with last time, I could have introduced all kinds of distortions, so take all this with a good dose of grains of salt. There was also plenty more interesting stuff that I saw but couldn't understand/contextualize well enough to put it into a post. (Lots of that was about Titan.)

Vesta's pole star is Deneb.

Titan seems to have seasonal rain in normally dry equatorial deserts.
There's a case made for Titan having dust storms.
Does Titan have ice volcanoes? Maybe, maybe not. Lots of things that looked like volcanoes at first seem not to be on closer inspection, but there's one good candidate: Sotra Facula.

Kuiper Belt Objects
Results from Eris occulting a star were presented, but couldn't be reported on Twitter due to an embargo :-( . They'll be published in Nature on Oct. 26th.

Makemake occulted a star with of magnitude V=18.2 on April 23, 2011. They observed the occultation with 7 telescopes in 5 locations, and found a drop in magnitude of 0.4. They were able to calculate Makemake's albedo as about 0.71, which is greater than Pluto's, and is consistent with the value of 0.81 derived from measurements the infrared telescopes Spitzer and Herschel. They calculate Makemake's size based on the occultation as about 1610 +22/-180 km x 1444+/-9 km. Whether or not the occultation data indicates an atmosphere is still being worked out.

Quaoar occulted a star too, and they observed it from at least 5 sites. Quaoar has is less reflective than was previously thought; this means that it's also larger and less dense. Its diameter is now estimated as 1045-1095 km, and density at 1.95-2.75 grams per cubic centimeter. It might have a methane atmosphere with a pressure of 0.1 ubar [I think ubar is an alternate abbreviation for µbar = microbar, but I'm not certain] at a temperature of 45K.

Extrasolar planets
The Kepler spacecraft's major measurements come from planets transiting their stars, but the measurements are also affected by how the planet and star distort each other tidally. Using these tidal distortions, it's possible figure out the mass ratio between the planet and the star just from observing transits. (Neat! It always amazes me how much information astronomers can squeeze out of a seemingly tiny bit of data.)

Upcoming missions
The European Space Agency's Solar Orbiter mission has been approved. It will orbit the sun in a highly inclined orbit inward of Mercury's orbit, and is expected to launch in 2017.

Other stuff
WISE shows 4 things that might potentially be very low mass brown dwarfs orbiting the sun. But they might also be extragalactic sources of radiation. (That's a big difference!)

Sources of tweets that I've used to compile this (again, I hope I haven't left anyone out):
[ profile] DrFunkySpoon
[ profile] GovertTweets
[ profile] AllPlanets
[ profile] elakdawalla
[ profile] PlanetDr
[ profile] spacemandave
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
I've been following on Twitter some of the things being reported at the joint conference of the American Astronomical Society's Division for Planetary Sciences and the European Planetary Science Congress (DPS-EPSC). I'm sure things will come out in a more refined form at some point, but here are some of the things reported that have caught my attention.

First of all, before my own extractions of stuff from Twitter, some stuff by people who know more than I do.

Emily Lakdawalla has written up a post on first impressions, including stuff from talks on Enceladus and Vesta. Some highlights mentioned in her post are: large salty grains in Enceladus's plumes make it pretty much certain that the plumes have a liquid source; Vesta doesn't have any moons larger than 10 metres diameter; and results for the mass, volume, density, and probable core size of Vesta. Also, Vesta's surprisingly colourful, as solar system objects go.

Three official press releases:
A press release about results from Dawn's mission to Vesta. An additional interesting piece of information from it is that surface temperatures have been measured from 240K to 270K. That's roughly -30° Celsius to 0° Celsius. (I'm assuming these are only dayside measurements, and that temperatures would become much colder during the night, but the press release doesn't actually say that.) There are lots of images and diagrams linked at the bottom of the press release.

And one on 'snow' (actually really really tiny ice particles) on Enceladus.

And a press release on the Kuiper Belt Object 2001 QG298. It's a contact binary - two objects touching each other. This was figured out in 2004 because of changes in its brightness when it rotated; it was rotating nearly edge-on to us, so that one of the two objects sometimes hid the other from view. At first they didn't know if it was rotating in the same plane as its orbit, in which case it would stay nearly edge on, or at an angle to its orbit, in which case the fact that we were seeing it edge on is because we're lucky enough to catch it at the right part of its object. Since it was discovered, the changes in brightness have diminished significantly, indicating that it's rotating nearly at right angles to its orbit, and thus we were just lucky to catch it. This hints that there may actually be a lot of contact binaries out there.

And now for some interesting tidbits from Twitter, sometimes with some context added; it's quite possible that I've gotten some things wrong in processing tweets into what I say below, so it should be taken with a good dose of grains of salt. Among other things, it's often hard to be sure from a tweet whether something is a tentative suggestion or something solidly evidenced.

About Vesta:
There are three kinds of meteorites on earth thought to come from Vesta: howardites, eucrites, and diogenites (grouped together as HED meteorites). Dawn's results so far indicate that the global spectrum of Vesta is more like that of howardites than of diogenites or eucrites. Regionally, the south of Vesta is more like diogenites than the north is. (The Wikipedia article on diogenites indicates that diogenites are thought to be from deep within Vesta. In that case, it makes sense that they would be found in the south, where the giant impact would remove a lot of the overlying surface.) Also, there are east/west differences in how eucrite-like Vesta is.

Spectral variations on Vesta are often associated with geological features, and spectra indicate the presence of pyroxene.

Vesta is estimated to have regolith 1.5-5 km deep; this estimate comes from crater shapes.

Dark material on Vesta occurs in craters, but also elsewhere. Where it comes from is still uncertain. Some possibilities: carbonaceous impactors, or volcanism, or both.

Initial indications are that Vesta has less water than Earth's Moon; this will be better determined once Vesta gets into Low Altitude Mapping Orbit.

About Titan:
The carbon isotope ratio on Titan is similar to that on Earth, according to Cassini data.

Titan's upper atmosphere has lots of heavy, negative ions. No one's sure yet how they get there.

The Huygens probe measured an electrical field in Titan's atmosphere that shows that Titan's crust is 60-80 km thick.

About Kuiper Belt Objects:
On 36% of KBOs, water ice has not been detected.

Varuna's thermal (infrared) lightcurve is correlated with its visible light lightcurve. I'm not entirely sure of the significance of this but I'm guessing that one thing it indicates is that the major variations in Varuna's lightcurve are due to its shape, and not to differences in how bright different parts of it are.

Twitter accounts I used in compiling the above (I hope I haven't forgotten any):
Emily Lakdawalla
David Minton
Franck Marchis
Europlanet Media
Meg Schwamb
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
A few years ago, there were some hints that Saturn's moons Tethys and Dione might have some sort of geological activity.

Follow-up observations to try to confirm this found no evidence of such activity, so it seems that they aren't active after all.
steorra: Part of Saturn in the shade of its rings (Default)
[personal profile] steorra
So, a few days ago, Dawn entered orbit around Vesta, and is now slowly spiralling in towards its intended science orbit. Already it has sent back some pictures that show interesting amounts of detail: this one from July 17 (press release for the image) and this one from July 18 (press release for the image).

Both pictures largely show the south polar terrain, where a large impact is believed to have taken quite a chunk off of Vesta; in the middle of the south polar terrain is a large peak.

What catches my attention is the texture of the south polar terrain. There are a lot of grooves and ridges that I suppose were probably formed in some way by the impact. There are craters on it, but it's not thoroughly cratered, which ought to indicate that it's not very very old. (It would be nice to see how cratered the rest of Vesta appears, for comparison, but the pictures we have so far don't show that very well; you can see a bit of the non-south-polar terrain in the July 17 picture.)

Pluto's moons
On Wednesday, the discovery of a fourth moon orbiting Pluto was announced! It was discovered with the Hubble Space Telescope.
steorra: Part of Saturn in the shade of its rings (Default)
[personal profile] steorra
There's something I want a word or phrase for, and I don't think there is one.

My main interest within astronomy is in the solar system. The objects in the solar system that I find most interesting are those that are big enough to be round (i.e., in hydrostatic equilibrium), but small enough to be solid - thus excluding the Sun and gas giants.

The objects that fit in my category of interest cut across several of the usual categories. It includes the terrestrial planets, but not the gas giants. It includes all dwarf planets. It includes relatively large moons (most moons with a diameter greater than about 400 km), but not small moons.

I've been calling them "solid round solar system bodies", but that's an awkward phrase and I'd really like a tidier one.

I was brainstorming with a friend the other day and the best we could come up with was something like "terrestrial worlds" or "terrestrial bodies". If I poke around on the internet to see how those phrases have been used before, they both seem to have several uses, none of which is quite what I'm looking for. One of the main issues with "terrestrial" is that it's sometimes used not to distinguish solid objects from gaseous objects, but to distinguish rocky solid bodies from icy solid bodies. But there are other uses of "terrestrial worlds" or "terrestrial bodies" that include both rocky and icy ones; the meaning I found closest to what I want included the terrestrial planets, Pluto, and the moons larger than Pluto, but for no apparent reason didn't include the round moons or dwarf planets (such as Ceres) that are smaller than Pluto.

What do you guys think? Is "terrestrial worlds" or "terrestrial bodies" a good term for the concept I want to name? Can you think of a better one?


Jun. 21st, 2011 12:42 pm
steorra: Part of Saturn in the shade of its rings (Default)
[personal profile] steorra
Lights in the Dark a neat blog of solar system photos by someone who, among other things, processes raw NASA images by e.g. combining images from different colour filters to produce a single colour image. This picture of Titan and Rhea is what led me there.

360° Io

May. 22nd, 2011 09:08 pm
steorra: Part of Saturn in the shade of its rings (Default)
[personal profile] steorra
A video of a rotating globe of Io.

(I got the link from today's Astronomy Picture of the Day, which features the Prometheus plume on Io.)
steorra: Part of Saturn in the shade of its rings (Default)
[personal profile] steorra
More Cassini articles, some of them old.
(I'm catching up on Cassini news that I haven't followed for a while, and posting some things that I find interesting.)

Titan seems to have no volcanoes after all, just weather. (Apr. 7, 2011)

'Cassini Catches Saturn Moons in Paintball Fight' (Oct. 7, 2010)

Pac-Man shaped thermal pattern on Mimas (March 29, 2010).

Also: The Enceladus atlas, as of May 13, 2010.
steorra: Part of Saturn in the shade of its rings (saturn)
[personal profile] steorra
I was trying to figure out if there is such a thing as a globe of Enceladus.

Someone made a globe of Enceladus on a grapefruit.



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