Poll: which Discovery mission would you vote for?

As a follow-on to the previous post, which newly proposed mission for NASA’s Discovery program would you like to see happen? Only one will be selected next year, to launch in 2016…

Sailing the seas of Titan

It was announced last week that there are three final mission proposals for NASA’s Discovery program, with one of them to be selected in 2012, for development and launch in 2016.

The first is the Geophysical Monitoring Station (GEMS) which would study the interior structure and composition of Mars. The second is the Titan Mare Explorer (TiME), which would land in and float on one the many methane lakes and seas on Titan. The third, Comet Hopper, would land on the same comet multiple times to observe changes over time.

Credit: NASA/JPL

There has been a lot of discussion about this, with most people opting for the Titan mission. And that would be my choice as well, since we’ve already been to Mars many times now (and more missions going there soon) and have observed numerous comets up close already by various spacecraft. But the chance to actually sail a boat as such on an alien sea, can we really pass that up? So far, Titan is the only other place known to have extensive rivers, lakes and seas on its surface. While being a much colder environment than anywhere on earth, some scientists have postulated the possibilty of some form of life there. Let’s go look…!

Is there still liquid water on Mars?

The question of whether liquid water can still exist today in Mars’ hostile climate has been around for decades, perhaps in underground aquifers or even for brief periods of time on the surface as salty brines. Debate still continues about the droplet-like features seen on one of the legs of the Phoenix lander, suggested by some members of the science team as possibly just such drops of liquid or partially liquid brines. Two recent papers from the 42nd Lunar and Planetary Science Conference this year further address the possibility of current liquid water.

The first looks at possible evidence for small seasonal pond-like features of saline (salty) water in the polar regions.

From the paper:

“Here we report the discovery of the spectral evidence for liquid water in flow-like and pond- like features of Mars polar region. This suggests that liquid saline water forms sporadically on the surface and should be common in the shallow subsurface.”

“More interestingly, measurements of the reflectance in different directions and therefore the albedo at the blue green (400-600 nm) and near infrared (780-1060 nm) portions of the spectrum show that ice, snow and soil have reflectances and albedo approximately constant with wavelength and that the reflectances and albedo of brines (melt ponds in sea ice) peaks at approximately 400-500 nm and decreases by almost an order of magnitude beyond 700 nm (Fig. 1). This happens because the absorption coefficient of liquid water is more than two orders of magnitude larger at near infrared than at blue green. In contrast, the reflectances and albedo of typical Mars soil is larger at near infrared, because it is rich in iron. Thus, the reflectances in a given direction or albedo at various portions of the spectrum, can be used to fingerprint liquid brines because it distinguishes them from frost, ice, snow, and soil.”

“HiRISE images of flow-like and pond-like features on polar dunes are analyzed by visually finding the brightest 25-50 pixels indicating frost/snow, the 25-50 darkest pixels in the darkest shadows, and adjusting the reflectance of each pixel with the aid of Eqn (7). Fig. 2 show that this analysis unveil the fingerprint of liquid water on Mars. Deliquescence occur in frost-covered areas that the temperature exceeds the eutectic temperature of salts in contact with it, before frost sublimates. This implies the existence of an optimum zone in the polar region where deliquescence occurs seasonally and produce surface flows and puddles of liquid saline water.”

The second paper suggests that salty brines may also still flow on the surface during the summer creating what are called “transient slope lineae.”

NASA / JPL / Univ. of Arizona

From the paper:

“In a companion abstract we describe HiRISE ob- servations of features we call transient slope lineae (TSL) [13]. TSL are defined as narrow (up to a few m wide) albedo markings on steep (>20°) slopes that are transient—present in some HiRISE images but not others. They extend downslope, typically from bedrock outcrops or from rocky areas, and are often associated with and may form small channels (Figure 1). TSL are very different from slope streaks that form on dust-mantled slopes, as summarized in Table 1.”

“Our favored model at present for TSL formation is that shallow brines mobilize thin flows, as first proposed for slope streaks [18]. To produce flows, there must be sufficient liquid to fill the pore space between particles; interfacial water [19] is not sufficient. The TSL mechanism may resemble that of [20], again for slope streaks, except that no runaway process is needed as TSL form incrementally. These flows may advance a little near the warmest time of each day, or they may advance by greater amounts on some days but not others.”

There is also a good blog post about these proposed TSLs on the Sky & Telescope web site (March 11). What’s interesting is that they seem to occur only on sun-facing slopes during mid-summer. Mars Reconnaissance Orbiter has observed them form and then change over time, starting out darker then gradually lightening in appearance.

Water? Only further observations will answer that question definitively.

First MESSENGER images from Mercury

The first spacecraft to ever orbit the innermost planet Mercury, MESSENGER, has started sending back some beautiful photos, the first of thousands to be taken over the course of the mission. Appearance-wise, Mercury is very similar to our moon, mostly gray and covered in craters, so perhaps not as exciting as the views from some of the other planetary locales in our solar system, but this mission is the first to study Mercury in unprecedented detail from the vantage point of orbit. As the MESSENGER web site notes, Mercury is “the smallest, the densest (after correcting for self-compression), the one with the oldest surface, the one with the largest daily variations in surface temperature, and the least explored.” That’s good enough for me to make it another interesting place to go to.

A few photos are posted below; additional ones are (and will be added) here.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Billions of worlds

New studies based on the results so far from the Kepler mission estimate that there are billions of other worlds out there, in our galaxy alone. The latest, from scientists at NASA’s Jet Propulsion Laboratory, indicates that 1.4 to 2.7 percent, or one out of every 37 to 70, of sun-like stars are expected to have planets similar in size to the Earth that orbit within the habitable zone of those stars, where temperatures could allow liquid water. That’s about 2 billion in just our galaxy. Also of note is that red dwarf stars can also have such planets, although harder to detect, and those stars are much more numerous than sun-like stars. The full paper (PDF) is here.

A previous recent estimate from Kepler scientists also puts the number of total planets in our galaxy, of various types, at 50 billion, and likely more than that according to Kepler science chief William Borucki. Then there are the at least 50 billion known galaxies.

It seems Carl Sagan knew what he was talking about when he used to say his famous phrase of “billions and billions”… how right he was.