Pale Blue Dot?
Water searches are done by a global enterprise of radio telescopes. For instance, largely because of the presence of frozen water in many comets (often characterized as "dirty snowballs"), comet clouds do present opportunities for water detection in the neighborhood of distant stars. In July of last year, a team of astronomers from Harvard, NASA/Ames and Johns Hopkins reported in Nature on circumstellar water around an aging carbon star (IRC+10216) and inferred the presence of icy bodies and cometary debris. So while the Italian team is seeking confirmation of their most recent conference publication from other researchers around the world, whether the water detection is a viable signal or not will hinge greatly on what is already known about their primary target, a triple-planet system orbiting Ups Andromedae.
A Triple-Planet System Orbiting Ups Andromedae
Located 44 light-years from Earth, the parent star itself (HD 9826) is probably a single star, although the Bright Star catalog lists it as a possible binary, but the star's motion is more consistent without including a companion. The star is approximately 1.2 times as massive as our Sun and around 2.6 billion years old (2/3 the age of our Sun). With its trio of planets, Upsilon Andromedae harbors the first planetary system that is reminiscent of our own Solar System.
"The usual picture is that gas giant planets form at least four AU away from a star, where temperatures are low enough for ice to condense and start the process of planet formation," said Timothy Brown of the High Altitude Observatory (HAO). "But all three giant planets around Upsilon Andromedae now reside inside this theoretical ice boundary." The planets may have formed close to the host star, or, like balls on a billiard table, the planets may have scattered off of each other, migrating into their current orbits from a more distant place of origin.
The inner planet, or "hot Jupiter" candidate, was first announced by Butler et al. in Jan 1997. This innermost of the three planets contains at least three-quarters of the mass of Jupiter and orbits only 0.06 AU from the star. It traverses a circular orbit every 4.6 days. The middle planet contains at least twice the mass of Jupiter and it takes 242 days to orbit the star once. It resides approximately 0.83 AU from the star, similar to the orbital distance of Venus. The outermost planet has a mass of at least four Jupiters and completes one orbit every 3.5 to 4 years, placing it 2.5 AU from the star. The two outer planets have elliptical (oval) orbits which is characteristic of other extrasolar planets in distant orbits around their stars.
All 3 planets are predicted roughly to have very high temperatures, based on standard reflection estimates (albedo like Jupiter, or 0.35) and their theorized orbits. From inner to outer planets found, the trio register temperatures of 1097 C (1947 F), 92 C (198 F), and -63 C (-81 F). Previous publications (Butler, et al. Astrophys. J) have noted that "Internal heating probably raises the temperature of the middle companion above the boiling point of water, while the outer companion is probably pushed up to near the water freezing point at a pressure of 1 atmosphere".
Robert Noyes, a professor of astronomy at Harvard-Smithsonian CfA and a member of the CfA-HAO team, said, "A nagging question was whether the massive bodies orbiting in apparent isolation around stars really are planets, but now that we see three around the same star, it is hard to imagine anything else."
If these Jupiter-mass planets are like our own Jupiter, they would not be expected to have solid Earth-like surfaces. But, Peter Nisenson of the Harvard-Smithsonian Center for Astrophysics (CfA) noted, "our observations can't rule out Earth-sized planets as well in this planetary system, because their gravity would be too weak for them to be detectable with present instruments."
Water Maser Emissions: Shock Physics
But for the more aged stars like Ups Andromedae, shockwaves are long subsided and another water source must be proposed. Detection of water registering as microwaves (or maser) signals at 22 gigahertz (Gz), Cosmovici wrote, yields "a powerful diagnostic tool for planetary search outside the Solar system".
In deep space, as the tiny wishbone-shaped water molecule (H2O) rotates around its central oxygen atom, a very high frequency resonance reaches microwave detectability. To record (or generate) these molecular rotations, a "maser" is the microwave equivalent of a laser, operating on (higher frequency) rotational energy states instead of vibrational states or electron shell jumps as in an ordinary light laser. (The name MASER stands for "Microwave Amplification by Stimulated Emission of Radiation", while laser is the "Light Amplification..." equivalent. )
Other possible targets for water detection around exoplanets included in Cosmovici's survey yield less certain probabilities of true planetary systems. Epsilon Eridani, a Sun-like star 10 light years away, and Lalande 21185, a red dwarf about 8 light years away, are both closer than the 44 light-year distance to Ups Andromedae but offer a less complete picture of what might be going on orbitally around those parent stars.
The star, Ups Andromedae should make an ideal target for NASA's upcoming Space Interferometry Mission (SIM). Expected to launch in 2005, SIM will spend five years probing nearby stars for Earth-sized planets and will test technology slated for future planet-searching telescopes. The ongoing ground-based planet search will enable SIM to home in on those stars most likely to harbor small planets.
References C.B.Cosmovici, S.Montebugnoli, A.Orfei, S.Pogrebenko and P.Colom, Planet.Space.Sci.,44,735,1996