Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2004 April 1 
Posted on 04/01/2004 5:22:08 AM PST by petuniasevan
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2004 April 1
Explanation: Today, April 1st, astrophysicists have announced a surprising discovery - April Fools Day is more intense on Mars! Though the discovery is contrary to accepted theories of April Fools Day, researchers note that there are several likely causes for the severe martian April Fools phenomenon. For starters, gravity, the force that opposes comedy throughout the universe, is only about 3/8ths as strong on Mars' surface as it is on planet Earth. Also, a martian day, called a sol, lasts nearly 40 minutes longer than an earth day. And furthermore ... well, as soon as they think of some more reasons, they've promised to tell us. Happy April Fools day from the editors at APOD! Editors note: Mars rover Spirit recorded this image looking out toward the eastern horizon and the Columbia Hills over 2 kilometers in the distance. Its journey across this rocky martian terrain could take from 60 to 90 sols.
Dozens of 'mini-galaxies' discovered by astronomers
ROYAL ASTRONOMICAL SOCIETY NEWS RELEASE
Posted: April 1, 2004
 UCDs may form via the destruction of larger galaxies, such as nucleated dwarf ellipticals. |
Now they say the UCDs outnumber the "conventional" elliptical and spiral galaxies in the central region of the Fornax cluster and they have found some in the Virgo galaxy cluster too. It is possible that at least some are left-over examples of the primordial "building blocks" that formed large galaxies by merging together. It is likely that they are very common but have been overlooked because they resemble nearby stars at first sight.
These results will be presented to the RAS National Astronomy Meeting at the Open University on Thursday by Dr Steven Phillips of Bristol University.
UCDs were discovered by chance when Dr Phillipps and his colleagues undertook a large survey of all the moderately bright objects they could see in the direction of the Fornax cluster. Only because they used a spectrograph (the Two Degree Field, or 2dF, system on the AAT) were they able to measure redshifts, which told them that 6 objects looking like local stars in our Galaxy were in fact in the Fornax cluster about 60 million light years away.
Follow-up observations with the Hubble Space Telescope and the European Southern Obervatory's Very Large Telescope (VLT) revealed just how strange they are. Although their masses are similar to those of previously known dwarf galaxies, they are amazingly small -- only about 120 light years across. Tens of millions of stars are squashed into what is a tiny volume by galaxy standards.
Favouring the idea that UCDs are the nuclei of galaxies that were originally larger and have been stripped of their outer stars, the team predicted that they would find them in other dense clusters where the stripping or "threshing" process could go on. They also calculated how many more they would expect to find if they searched for fainter ones.
When they put their predictions to the test, 3 nights of observations uncovered a further 46 UCDs in Fornax -- even more than the team had expected -- and in just 4 hours they found 8 in the Virgo cluster, also around 60 million light years away.
"These results indicate that UCDs are indeed common," says Steve Phillipps, "and part of the standard population of galaxies we can expect in rich galaxy clusters. Given that we found so many, it is even possible that a proportion of them are the remnants of a population of primordial galaxies, remnants of the original building blocks of the large galaxies we find at the centres of clusters.
Ocean waves forecast for Saturn's moon Titan
ROYAL ASTRONOMICAL SOCIETY NEWS RELEASE
Posted: March 31, 2004
 An artist's concept of the Huygens probe descending through Titan's atmosphere. Credit: ESA |
In what is probably the first piece of "extraterrestrial oceanography" ever carried out, Dr Nadeem Ghafoor of Surrey Satellite Technology and Professor John Zarnecki of the Open University, with Drs Meric Srokecz and Peter Challenor of the Southampton Oceanography Centre, calculated how any seas on Titan would compare with Earth's oceans. Their results predict that waves driven by the wind would be up to 7 times higher but would move more slowly and be much farther apart.
Dr Ghafoor will present their findings at the RAS National Astronomy Meeting at the Open University on Wednesday.
The team worked with a computer simulation, or 'model', that predicts how wind-driven waves on the surface of the sea are generated on Earth, but they changed all the basic inputs, such as the local gravity, and the properties of the liquid, to values they might expect on Titan.
Arguments about the nature of Titan's surface have raged for a number of years. Following the flyby of the Voyager 1 spacecraft in 1980, some researchers suggested that Titan's concealed surface might be at least partly covered by a sea of liquid methane and ethane. But there are several other theories, ranging from a hard icy surface at one extreme to a near-global hydrocarbon ocean at the other. Other variants include the notion of hydrocarbon 'sludge' overlying an icy surface.
Planetary scientists hope that the Cassini/Huygens mission will provide an answer to this question, with observations from Cassini during several flybys of Titan and from Huygens, which will land (or 'splash') on 14 January 2005.
The idea that Titan has significant bodies of surface liquid has recently been reinforced by the announcement that radar reflections from Titan have been detected using the giant Arecibo radio dish in Puerto Rico.
Importantly, the returned signals in 12 out the 16 attempts made contained reflections of the kind expected from a polished surface, like a mirror. (This is similar to seeing a blinding patch of light on the surface of the sea where the Sun is being reflected.) The radar researchers concluded that 75% of Titan's surface may be covered by 'open bodies of liquid hydrocarbons' -- in other words, seas.
The exact nature of the reflected radar signal can be used to determine how smooth or choppy the liquid surface is. This interpretation says that the slope of the waves is typically less than 4 degrees, which is consistent with the predictions of the British scientists, who showed that the maximum possible slope of waves generated by wind speeds up to 7 mph would be 11 degrees.
"Hopefully ESA's Huygens probe will end the speculation" says Dr Ghafoor. "Not only will this be by far the most remote soft landing of a spacecraft ever attempted but Huygens might become the first extraterrestrial boat if it does indeed land on a hydrocarbon lake or sea."
Although not designed specifically to survive landing or to float, the chances it will do so are reasonable. However, the link back to Earth from Huygens via Cassini, which will be flying past Titan and acting as a relay, will only last for a maximum of 2 hours. During this time, if the probe is floating on a sea, one of the 6 instruments Huygens is carrying, the Surface Science Package experiment, which is led by John Zarnecki, will be making oceanography measurements. Among the 9 sensors that it carries are ones that will measure the height and frequency of the waves and also the depth of the sea using sonar. It will also attempt to determine the composition of the sea.
What would the sea look like?
"Huygens does carry a camera so it is possible we shall have some direct images," says Professor Zarnecki, "but let's try to imagine that we are sitting onboard the probe after it has landed in a Titan ocean. What would we see? Well, the waves would be more widely dispersed than on Earth but they will be very much higher - mostly as a result of the fact that Titan gravity is only about 15% of that on Earth. So the surface around us would probably appear flat and deceptively calm, but in the distance we might see a rather tall, slow-moving wave advancing towards us -- a wave that could overwhelm or sink us."
YES! You too can be added to the APOD PING list! Just ask!
(Great cartoon!)
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.