Lost lakes of Titan are found at last January 5, 2007
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Lakes of methane have been spotted on Saturn’s largest moon, Titan, boosting the theory that this strange, distant world bears beguiling similarities to Earth, according to a new study.
Titan has long intrigued space scientists, as it is the only moon in the Solar System to have a dense atmosphere — and its atmosphere, like Earth’s, mainly comprises nitrogen.
Titan’s atmosphere is also rich in methane, although the source for this vast store of hydrocarbons is unclear.
Methane, on the geological scale, has a relatively limited life. A molecule of the compound lasts several tens of millions of years before it is broken up by sunlight.
Given that Titan is billions of years old, the question is how this atmospheric methane gets to be renewed. Without replenishment, it should have disappeared long ago.
A popular hypothesis is that it comes from a vast ocean of hydrocarbons.
But when the US spacecraft Cassini sent down a European lander, Huygens, to Titan in 2005, the images sent back were of a rugged landscape veiled in an orange haze.
There were indeed signs of methane flows and methane precipitation, but nothing at all that pointed to any sea of the stuff.
But a flyby by Cassini on July 22 last year has revealed, thanks to a radar scan, 75 large, smooth, dark patches between three and 70 kilometers across (two and 42 miles) across that appear to be lakes of liquid methane, scientists report on Thursday.
They believe the lakes prove that Titan has a “methane cycle” — a system that is like the water cycle on Earth, in which the liquid evaporates, cools and condenses and then falls as rain, replenishing the surface liquid.
As on Earth, Titan’s surface methane may well be supplemented by a “table” of liquid methane that seeps through the rock, the paper suggests.
Some of the methane lakes seem only partly filled, and other depressions are dry, which suggests that, given the high northerly latitudes where they were spotted, the methane cycle follows Titan’s seasons.
In winter, the lakes expand, while in summer, they shrink or dry up completely — again, another parallel with Earth’s hydrological cycle.
The study, which appears on Thursday in the British weekly journal Nature, is headed by Ellen Stofan of Proxemy Research in Virginia and University College London.
Titan and Earth are of course very different, especially in their potential for nurturing life. Titan is frigid, dark and, as far as is known, waterless, where as Earth is warm, light and has lots of liquid water.
But French astrophysicist Christophe Sotin says both our planet and Titan have been sculpted by processes that, fundamentally, are quite similar.
The findings “add to the weight of evidence that Titan is a complex world in which the interaction between the inner and outer layers is controlled by processes similar to those that must have dominated the evolution of any Earth-like planet,” Sotin said in a commentary.
“Indeed, as far as we know,” Sotin added, “there is only one planetary body that displays more dynamism than Titan. Its name is Earth.”
[SOURCE: PARIS AFP http://news.yahoo.com/s/afp/20070103/sc_afp/spacesaturntitan_070103193516 ]
HAT-P-1 – Largest and Least Dense Planet found September 15, 2006
Posted by muneeb in Planets.4 comments
Using a network of small, automated telescopes known as HAT, Smithsonian astronomers have discovered a planet unlike any other known world. This new planet, designated HAT-P-1, orbits one member of a pair of distant stars 450 light-years away in the constellation Lacerta.
“We could be looking at an entirely new class of planets,” said Gaspar Bakos, a Hubble fellow at CfA. Bakos designed and built the HAT network and is lead author of a paper submitted to the Astrophysical Journal describing the discovery
With a radius about 1.38 times Jupiter’s, HAT-P-1 is the largest known planet. In spite of its huge size, its mass is only half that of Jupiter.
“This planet is about one-quarter the density of water,” Bakos said. “In other words, it’s lighter than a giant ball of cork! Just like Saturn, it would float in a bathtub if you could find a tub big enough to hold it, but it would float almost three times higher.”
HAT-P-1’s parent star is one member of a double-star system called ADS 16402 and is visible in binoculars. The two stars are separated by about 1500 times the Earth-Sun distance. The stars are similar to the Sun but slightly younger – about 3.6 billion years old compared to the Sun’s age of 4.5 billion years.
Although stranger than any other extrasolar planet found so far, HAT-P-1 is not alone in its low-density status. The first planet ever found to transit its star, HD 209458b, also is puffed up about 20 percent larger than predicted by theory. HAT-P-1 is 24 percent larger than expected.
“Out of eleven known transiting planets, now not one but two are substantially bigger and lower in density than theory predicts,” said co-author Robert Noyes (CfA). “We can’t dismiss HD209458b as a fluke. This new discovery suggests something could be missing in our theories of how planets form.”
IAU 2006 General Assembly: Result of the IAU Resolution votes August 29, 2006
Posted by muneeb in IAU, Planets.add a comment
24 August 2006, Prague: The first half of the Closing Ceremony of the 2006 International Astronomical Union (IAU) General Assembly has just concluded. The results of the Resolution votes are outlined here.
It is official: The 26th General Assembly for the International Astronomical Union was an astounding success! More than 2500 astronomers participated in six Symposia, 17 Joint Discussions, seven Special Sessions and four Special Sessions. New science results were vigorously discussed, new international collaborations were initiated, plans for future facilities put forward and much more.
In addition to all the exciting astronomy discussed at the General Assembly, six IAU Resolutions were also passed at the Closing Ceremony of the General Assembly:
Resolution 1 for GA-XXVI: “Precession Theory and Definition of the Ecliptic”
Resolution 2 for GA-XXVI: “Supplement to the IAU 2000 Resolutions on reference systems”
Resolution 3 for GA-XXVI: “Re-definition of Barycentric Dynamical Time, TDB”
Resolution 4 for GA-XXVI: “Endorsement of the Washington Charter for Communicating Astronomy with the Public”
Resolution 5A: “Definition of ‘planet’ “
Resolution 6A: “Definition of Pluto-class objects”
The IAU members gathered at the 2006 General Assembly agreed that a “planet” is defined as a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
This means that the Solar System consists of eight “planets” Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A new distinct class of objects called “dwarf planets” was also decided. It was agreed that “planets” and “dwarf planets” are two distinct classes of objects. The first members of the “dwarf planet” category are Ceres, Pluto and 2003 UB313 (temporary name). More “dwarf planets” are expected to be announced by the IAU in the coming months and years. Currently a dozen candidate “dwarf planets” are listed on IAU’s “dwarf planet” watchlist, which keeps changing as new objects are found and the physics of the existing candidates becomes better known.
The “dwarf planet” Pluto is recognised as an important proto-type of a new class of trans-Neptunian objects. The IAU will set up a process to name these objects.
Results:
Resolution 5A: “Definition of Planet” was not counted but was passed with a great majority.
Resolution 5B: “Definition of Classical Planet” had 91 votes in favour, but many more against so there was no count.
Resolution 6A: “Definition of Pluto-class objects” was passed with 237 votes in favour, 157 against and 17 abstentions.
Resolution 6B: “Definition of Plutonian Objects” had 183 votes in favour and 186 votes against.
RESOLUTIONS
Resolution 5A is the principal definition for the IAU usage of “planet” and related terms.
Resolution 6A creates for IAU usage a new class of objects, for which Pluto is the prototype. The IAU will set up a process to name these objects.
IAU Resolution: Definition of a Planet in the Solar System
Contemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation “planets”. The word “planet” originally described “wanderers” that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.
RESOLUTION 5A
The IAU therefore resolves that “planets” and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way:
(1) A “planet”1 is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
(2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape2 , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
(3) All other objects3 except satellites orbiting the Sun shall be referred to collectively as “Small Solar-System Bodies”.
1The eight “planets” are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
2An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
3These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.
IAU Resolution: Pluto
RESOLUTION 6A
The IAU further resolves:
Pluto is a “dwarf planet” by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.
[SOURCE: http://www.iau.org/iau0603.414.0.html ]
