20 May 2011

Finding Neptune and Uranus

In the early morning hours these days we can spot Mercury, Venus, Mars and Jupiter without any optical aid. But there are two giants who rise early but require little optical help, these giants are, planets Neptune and Uranus.

If we look at the eastern sky at around 3am the planet Neptune will be at an altitude of 40degree from the eastern horizon in the constellation of Aquarius. One advantage of spotting the planet at this time of 3am is that we have bright 1st magnitude star Fomalhaut as a reference starting point. Looking at south-east the star Fomalhaut can be easily found as there are no bright 1st magnitude stars other than Fomalhaut in that region.

We will start by locating the star Fomalhaut, the sky charts below will be of good help. 
 The sky is for 3:30am.

Once we have Fomalhaut in the field of binocular or telescope, we move up 21 degrees and locate delta Capricorni, follow the dotted yellow line.  

Delta Capricorni is an 2.8 magnitude star and can be easily found. Now from Delta Capricorni we move to Iota Aquarii.

Iota Aquarii  is little dimmer at 4.2magnitude and it is around 5degrees NE from Delta Capricorni. From Iota Aquarri we move 2.3degrees North and find the star 38 Aquarii at magnitude 5.4.

Neptune lies just 21 minutes east of 38 Aquarii (below 38 Aquarii) and is easy to spot. At opposition the distance from Earth 4347.31 million(km). The Apparent Magnitude of the planet is 7.8 magnitude.

Rising times of Neptune:

28 May 2011 00:20
05 Jun 2011 23:45
13 Jun 2011 23:13
21 Jun 2011 22:42
29 Jun 2011 22:10
07 Jul 2011 21:38
15 Jul 2011 21:05
23 Jul 2011 20:34
31 Jul 2011 20:02
08 Aug 2011 19:30


Uranus is easy to find as the planet is bright at 5.9 magnitude. These charts will help in locating the planet. We all are very familiar with the Great Square, using the two stars Alpheratz and Algenib and moving towards south, its easy to find the planet Uranus. At opposition the distance  2719 million (km) and shines at a 5.5magnitude.

The sky at 3:30am

Rising Times of Uranus:

28 May 2011 02:11:00 AM
05 Jun 2011 01:40:00 AM
13 Jun 2011 01:10:00 AM
21 Jun 2011 12:39:00 AM
29 Jun 2011 12:08:00 AM
07 Jul 2011 11:32:00 PM
15 Jul 2011 11:01:00 PM
23 Jul 2011 10:29:00 PM
31 Jul 2011 09:57:00 PM
08 Aug 2011 09:25:00 PM

Happy spotting the planets and clear skies.

Star chart prepared with Stellarium 

19 May 2011

Free-Floating Planets May Be More Common Than Stars

Astronomers have discovered a new class of Jupiter-sized planets floating alone in the dark of space, away from the light of a star. The team believes these lone worlds are probably outcasts from developing planetary systems and, moreover, they could be twice as numerous as the stars themselves.
Artist's conception illustrates a Jupiter-like planet  Image credit: NASA/JPL-Caltech
"Although free-floating planets have been predicted, they finally have been detected," said Mario Perez, exoplanet program scientist at NASA Headquarters in Washington. "[This has] major implications for models of planetary formation and evolution."
The discovery is based on a joint Japan-New Zealand survey that scanned the center of the Milky Way galaxy during 2006 and 2007, revealing evidence for up to 10 free-floating planets roughly the mass of Jupiter. The isolated orbs, also known as orphan planets, are difficult to spot, and had gone undetected until now. The planets are located at an average approximate distance of 10,000 to 20,000 light years from Earth.

This could be just the tip of the iceberg.  The team estimates there are about twice as many free-floating Jupiter-mass planets as stars. In addition, these worlds are thought to be at least as common as planets that orbit stars. This adds up to hundreds of billions of lone planets in our Milky Way galaxy alone.
"Our survey is like a population census," said David Bennett, a NASA and National Science Foundation-funded co-author of the study from the University of Notre Dame in South Bend, Ind. "We sampled a portion of the galaxy, and based on these data, can estimate overall numbers in the galaxy."
The study, led by Takahiro Sumi from Osaka University in Japan, appears in the May 19 issue of the journal Nature. The survey is not sensitive to planets smaller than Jupiter and Saturn, but theories suggest lower-mass planets like Earth should be ejected from their stars more often. As a result, they are thought to be more common than free-floating Jupiters.
Previous observations spotted a handful of free-floating planet-like objects within star-forming clusters, with masses three times that of Jupiter. But scientists suspect the gaseous bodies form more like stars than planets. These small, dim orbs, called brown dwarfs, grow from collapsing balls of gas and dust, but lack the mass to ignite their nuclear fuel and shine with starlight. It is thought the smallest brown dwarfs are approximately the size of large planets.
On the other hand, it is likely that some planets are ejected from their early, turbulent solar systems, due to close gravitational encounters with other planets or stars. Without a star to circle, these planets would move through the galaxy as our sun and others stars do, in stable orbits around the galaxy's center. The discovery of 10 free-floating Jupiters supports the ejection scenario, though it's possible both mechanisms are at play.
"If free-floating planets formed like stars, then we would have expected to see only one or two of them in our survey instead of 10," Bennett said. "Our results suggest that planetary systems often become unstable, with planets being kicked out from their places of birth."
The observations cannot rule out the possibility that some of these planets may be in orbit around distant stars, but other research indicates Jupiter-mass planets in such distant orbits are rare.
The survey, the Microlensing Observations in Astrophysics (MOA), is named in part after a giant wingless, extinct bird family from New Zealand called the moa. A 5.9-foot (1.8-meter) telescope at Mount John University Observatory in New Zealand is used to regularly scan the copious stars at the center of our galaxy for gravitational microlensing events. These occur when something, such as a star or planet, passes in front of another more distant star. The passing body's gravity warps the light of the background star, causing it to magnify and brighten. Heftier passing bodies, like massive stars, will warp the light of the background star to a greater extent,resulting in brightening events that can last weeks. Small planet-size bodies will cause less of a distortion, and brighten a star for only a few days or less.
A second microlensing survey group, the Optical Gravitational Lensing Experiment (OGLE), contributed to this discovery using a 4.2-foot (1.3 meter) telescope in Chile. The OGLE group also observed many of the same events, and their observations independently confirmed the  analysis of the MOA group.

Source and Credit: Science@NASA

18 May 2011

At the Heart of Hartley-2, a New Breed of Comet?

At the heart of every comet lies a remnant of the dawn of the solar system. Or is that remnants? Astronomers don't know, but the answer would give them a clearer picture of exactly how comets were born eons ago at the birth of the Solar System. Did thin tendrils of dust and ice get drawn slowly inward and pack themselves into a single, uniform mass? Or did a hodge-podge of mini-comets come together to form the core for a comet of substance?
This close-up view of comet Hartley 2 was taken by NASA's EPOXI mission during its flyby of the comet. It was captured by the spacecraft's Medium-Resolution instrument. Last Update: 28 Mar 2011 (AMB)
Credit: NASA/JPL-Caltech/UMD

For Hartley-2, the answer so far is neither. "We haven't seen a comet like this before," says Michael Mumma of NASA's Goddard Space Flight Center in Greenbelt, Md. "Hartley-2 could be the first of a new breed."
Both data collected by Mumma's team and detailed images of the comet taken by NASA's EPOXI mission reveal that the comet's core is not uniform. "We have evidence of two different kinds of ice in the core, possibly three," says Mumma. "But we can also see that the comet's overall composition is very consistent. So, something subtle is happening. We're not sure what that is."

The researchers observed Hartley-2 six times during the summer, fall and winter of 2010, both before and after the EPOXI mission's Deep Impact spacecraft had its November rendezvous with the comet. Using telescopes perched high in the mountains of Hawaii and Chile, Mumma's team studied the comet's coma-the aura of gas, dust and ice particles that surround the core. The findings of Mumma and his colleagues at Catholic University of America in Washington, D.C., the University of Missouri in St. Louis, the University of Hawaii in Honolulu, the California Institute of Technology in Pasadena, the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany, and Rowan University in Glassboro, N.J., are being reported in a special issue of Astrophysical Journal Letters on May 16, 2011
Jets spew out ice and carbon dioxide from one end of comet Hartley-2 in this EPOXI image, while water vapor gets released from the middle region. The differences suggest that the comet's core is made of at least two different ices. Ground-based measurements suggest the presence of a third ice. Credit: NASA/JPL-Caltech/UMD.

The gases and rocky particles that make up the coma are the clues that astronomers use to deduce what the core is made of, and thus its origin. To see which types of molecules are there, researchers check for telltale signatures in the near-infrared region of light, at wavelengths from 2.9 to 3.8 micrometers. In this way, it's also possible to tell how plentiful each type of molecule is.

Ices in Hartley-2 are mostly made of water, along with traces of many other types of molecules, the team learned. This is in addition to the plentiful carbon dioxide detected in the comet in 1997 by the European Space Agency's Infrared Space Observatory. Mumma and colleagues paid close attention to the levels of water and seven other molecules that evaporate easily. The molecules remain frozen either on or below the core's surface until the warming rays of the sun vaporize them; then, they are swept into the coma.

The release of the molecules depends a great deal on exposure to the sun. The researchers knew that in 2009 ground-based observers had detected telltale signs that the core was rotating quickly. So the team was interested in what would happen to the production levels of these molecules as the comet rotated every 18 hours, giving each of its faces a turn to bathe in sunlight. Turns out, they saw something that nobody has seen before.
First of all, they saw the comet's wild side. "The amount of water changed dramatically night by night and even within a single night-in some cases, doubling in that time," says Mumma. But, in truth, Hartley-2 isn't the only comet to get caught being fickle.

What surprised the researchers was this: as the amount of water went up, so did the amounts of the other gases. And as the amount of water went down, the others did, too. "This is the first time anyone has seen an entire suite of these gases change in the same way at the same time," says Mumma.
This result is important for astronomers, he notes, because they often study the gases in a comet's coma one at a time. "But this suggests that if you look at one gas on one night and another the next night, the production rates might change quite a bit. The findings could be different than if you measured the two gases together," he says. "And in the worst case, you could get the wrong idea about the composition of the comet."
Beyond that, Mumma says, "this tells us that the overall composition of the gas in the coma did not change." Taken by itself, this might seem to imply that the core of the comet is uniform. But when the findings of the EPOXI science team are considered, the picture gets more complicated.

"The fact that the gases all vary together is somewhat puzzling, because EPOXI found a large variation in the release of carbon dioxide relative to water," says the head of the EPOXI science team, Michael A'Hearn of the University of Maryland. "At this point the interpretation is pretty speculative."
EPOXI's Deep Impact spacecraft had a rendezvous with the comet in November 2010. The rich images taken then of the comet's surface revealed small, volcano-like "jets" spewing out carbon dioxide gas and water ice at one end. The jets activate when sunlight warms that end of the comet, turning the frozen carbon dioxide (aka dry ice) below the surface into gas that escapes through open holes.
The researchers think that chunks of water ice are glued together in the comet's core by the frozen carbon dioxide, which evaporates before the water ice. "The carbon dioxide gas drags with it chunks of ice, which later evaporate to provide much of the water vapor in the coma," A'Hearn explains.
Researchers had never seen this before. "In other comets that have been visited, most of the water appears to be converted into gas below or at the surface," says A'Hearn. "We have not seen icy grains, or at least, very few, being dragged into the coma."

But the whole core is not made the same way. EPOXI revealed that the carbon dioxide jets are not found at the large end of the comet, and in the middle region, water vapor is released without any carbon dioxide. "So clearly, when we look at the comet up close, the composition of the core changes from one region to another," Mumma says.

Mumma's team found more evidence that Hartley-2's core is not uniform. They did so by looking carefully at four types of gas to see in which directions their molecules traveled after release. They saw that water and another gas, methanol, came off the comet in all directions. "Because they are found together, we infer that they come from the same chunks of ice," he explains.

"So, we have water ice with methanol in it, and we have carbon dioxide ice. Both are in the comet's core," Mumma says. "We may also have a third type of ice, made from ethane."
That possibility is based on the fact that ethane, unlike water and methanol, was released strongly in one direction. "This is actually rather profound," says Mumma. "It suggests that some molecules, such as methanol, may be mixed with water, while others, such as ethane, are not. This isn't the way we've thought of comets, before now."

More research needs to be done, and whether all comets behave like Hartley-2 isn't known, Mumma adds. "But now that we know what this one does, we have a baseline to compare other comets against."

Elizabeth Zubritsky
NASA's Goddard Space Flight Center, Greenbelt, Md