* Astronomy

Title: WASP-1b and WASP-2b: Two new transiting exoplanets detected with SuperWASP and SOPHIE
Authors: A. Collier Cameron, F. Bouchy, G. Hebrard, P. Maxted, D. Pollacco, F. Pont, I. Skillen, B. Smalley, R. A. Street, R.G. West, D.M. Wilson, S. Aigrain, D.J. Christian, W.I. Clarkson, B. Enoch, A. Evans, A. Fitzsimmons, M. Gillon, C.A. Haswell, L. Hebb, C. Hellier, S.T. Hodgkin, K. Horne, J. Irwin, S.R. Kane, F.P. Keenan, B. Loeillet, T.A. Lister, M. Mayor, C. Moutou, A.J. Norton, J. Osborne, N. Parley, D. Queloz, R. Ryans, A.H.M.J. Triaud, S. Udry, P.J. Wheatley

We have detected radial-velocity variations in two objects that were identified as being likely host stars of transiting exoplanets in the 2004 SuperWASP wide-field transit survey. Using the newly-commissioned radial-velocity spectrograph SOPHIE at the Observatoire de Haute-Provence, we found that both objects exhibit reflex orbital radial-velocity variations with amplitudes characteristic of planetary-mass companions and in-phase with the photometric orbits. Line-bisector studies rule out faint blended binaries as the cause of either the radial-velocity variations or the transits. We perform preliminary spectral analyses of the host stars, which together with their radial-velocity variations and fits to the transit light curves, yield estimates of the planetary masses and radii. WASP-1b and WASP-2b have orbital periods of 2.52 and 2.15 days respectively. Given mass estimates for their F7V and K1V primaries we derive planet masses 0.80 to 0.98 and 0.81 to 0.95 times that of Jupiter respectively. WASP-1b appears to have an inflated radius of at least 1.33 R_Jup, whereas WASP-2b has a radius in the range 0.65 to 1.26 R_Jup.

Read more (44kb, PDF)

(revised v2): Sat, 7 Oct 2006 10:09:34 GMT

-- Edited by Blobrana at 10:44, 2006-10-10

An international team of astronomers has found the smallest Earth-like planet yet outside our Solar System.

The new planet has five times the Earth's mass and can be found about 25,000 light-years away in the Milky Way, orbiting a red dwarf star.
The discovery, reported in the journal Nature, was made using a method called microlensing, which can detect far-off planets with an Earth-like mass.
The planet's cold temperatures make the chance of finding life very unlikely.
The planet, which goes by the name OGLE-2005-BLG-390Lb, takes about 10 years to orbit its parent star, a red dwarf which is cooler and smaller than Earth's Sun.
It is in the same galaxy as Earth, the Milky Way, but is found closer to the galactic centre.

The scientists say it probably has a rocky core and perhaps even a thin atmosphere, but its large orbit and cool parent star mean it is a very cold world.
Predicted surface temperatures are minus 220 degrees Celsius, meaning that its surface is likely to be layer of frozen liquid. It may therefore resemble a more massive version of Pluto.

"This is very exciting and important. This is the most Earth-like planet we have discovered to date, in terms of its mass and the distance from its parent star. Most of the other planets that have been discovered are either much more massive, much hotter or both" - Professor Michael Bode from Liverpool John Moores University, a principal investigator for the RoboNet project which collaborated on this research.

The microlensing technique used to find this planet was first predicted by Albert Einstein in 1912.
Microlensing occurs when a massive object in space, like a star, crosses in front of another more distant star.
As it passes, the gravity from the foreground object bends the light coming from the background star, temporarily making it look brighter. This usually lasts for about a month.
If the foreground star has a planet orbiting it, it will distort the light even more, and will make the star behind it look even brighter. But this effect lasts for a much shorter period, giving astronomers just hours or days to detect it.
Dr Martin Dominik from the University of St Andrews is a co-leader of the PLANET collaboration, one of the microlensing networks used to detect the new planet.

"We first saw the usual brightening reaching a peak magnification on 31 July 2005. On 10 August, however, there was a small 'flash' lasting about half a day. By succeeding in catching this anomaly with two of the telescopes of our network and with careful monitoring, we were able to conclude that the lens star is accompanied by a low-mass planet" - Dr Martin Dominik.

The discovery was the joint effort of three microlensing campaigns, PLANET/RoboNet, OGLE and MOA, and involved researchers from 12 countries.
So far, about 160 planets have been found outside our Solar System, but only three of them have been located using the microlensing technique.
Recent simulations of planet formation suggest that bodies with an Earth-like mass are abundant. Scientists are attempting to discover more new worlds using this technique and are looking for ways to refine it further.

"We could take this research forward by building a network of bigger telescopes around the world to make us more efficient at detecting these Earth-like planets" - Dr Nicholas Rattenbury, from Jodrell Bank Observatory in Cheshire, a member of the MOA microlensing collaboration.

If planets are found with conditions similar to our own planet, then the next step would be to begin the search for life, but this might not prove easy.

"To prove there is life on a far-off planet would be difficult. How can we prove there is life on a distant planet when we have problems seeing if there is life on Mars?" - Dr Martin Dominik.

Source

It is only a matter of time before astronomers find an Earth-sized planet orbiting a distant star. When they do, the first questions people will ask are: Is it habitable? And even more importantly, is there life present on it already? For clues to the answers, scientists are looking to their home planet, Earth.
Astronomers Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics (CfA) and Wesley Traub of NASA's Jet Propulsion Laboratory and CfA, propose using Earth's atmospheric history to understand other planets.

"Good planets are hard to find. Our work provides the signposts astronomers will look for when examining truly Earth-like worlds" - Lisa Kaltenegger

Geologic records show that Earth's atmosphere has changed dramatically during the past 4.5 billion years, in part because of life forms developing on our planet. Mapping what gases comprised Earth's atmosphere during its history, Kaltenegger and Traub propose that by looking for similar atmospheric compositions on other worlds, scientists will be able to determine if that planet has life on it, and if so, that life's evolutionary stage.
To date, all extrasolar planets have been studied indirectly, for example by monitoring the way a host star wobbles as the planet's gravity tugs it. Only four extrasolar planets have been detected directly, and they are massive Jupiter-sized worlds. The atmosphere of one of these worlds was detected by another CfA scientist, David Charbonneau, using NASA's Spitzer Space Telescope. The next generation of space-based missions such as NASA's Terrestrial Planet Finder (TPF) and ESA's Darwin will be able to directly study nearby Earth-sized worlds.
Astronomers particularly want to observe the visible and infrared spectra of distant terrestrial planets to learn about their atmospheres. Particular gases leave signatures in a planet's spectrum, like fingerprints or DNA markers. By spotting those fingerprints, researchers can learn about an atmosphere's composition and even deduce the presence of clouds.
Today, Earth's atmosphere consists of about three-fourths nitrogen and one-fourth oxygen, with a small percentage of other gases like carbon dioxide and methane. But four billion years ago, no oxygen was present. Earth's atmosphere has evolved through six distinct epochs, each characterized by a particular mix of gases. Using a computer code developed by Traub and CfA colleague Ken Jucks, Kaltenegger and Traub modelled each of Earth's six epochs to determine what spectral fingerprints would be seen by a distant observer.

"By studying Earth's past, we can learn about the present state of other worlds. If an extrasolar planet is found with a spectrum similar to one of our models, we potentially could characterise that planet's geological state, its habitability, and the degree to which life has evolved on it" - Wesley Traub.

To better understand these time periods, or "epochs," and to put them into perspective, one can scale the Earth's 4.5-billion-year history down to one year, attaching dates beginning with January 1 - the date the Earth formed.

EPOCH 0 - February 12
At Epoch 0 (3.9 billion years ago), the young Earth possessed a turbulent, steamy atmosphere composed mostly of nitrogen, carbon dioxide and hydrogen sulphide. The days were shorter and the Sun was dimmer, shining as a red orb through our orange brick-coloured sky. The one ocean that covered our entire planet was a muddy brown that absorbed bombardment from incoming meteors and comets. Carbon dioxide helped warm our world since the infant Sun was a third less luminous than today. Although no fossils survived from this time period, isotopic signatures of life may have been left behind in Greenland rocks.

EPOCH 1 - March 17
About 3.5 billion years ago (Epoch 1), the planet landscape featured volcanic island chains poking out of the vast global ocean. The first life on Earth was anaerobic bacteria - bacteria that could live without oxygen. These bacteria pumped large amounts of methane into the planet's atmosphere, changing it in detectable ways. If similar bacteria exist on another planet, future missions like TPF and Darwin could detect their fingerprint in the atmosphere.

EPOCH 2 - June 5
About 2.4 billion years ago (Epoch 2), the atmosphere reached its maximum methane concentration. The dominant gases were nitrogen, carbon dioxide, and methane. Continental landmasses were beginning to form. Blue green algae began pumping large amounts of oxygen into the atmosphere. Big changes were about to happen.

"I'm sorry to say the first signs of E.T. probably won't be a radio or TV broadcasts; instead, it could be oxygen from algae" - Lisa Kaltenegger .

EPOCH 3 - July 16
Two billion years ago (Epoch 3), these first photosynthetic organisms shifted the atmosphere's balance permanently-they produced oxygen, a highly reactive gas that cleared out much of the methane and carbon dioxide, while also suffocating the anaerobic, methane-producing bacteria. In doing so, the planet's atmosphere gained its first free oxygen. The landscape now was flat and damp. With volcanoes smoking in the distance, brilliantly coloured pools of greenish-brown scum created a sheen on the stench-filled water. The oxygen revolution was fully underway.

"The introduction of oxygen was catastrophic to the dominant life on Earth at that time; it poisoned it. But at the same time, it made multicellular life, including human life, possible" - Wesley Traub.

EPOCH 4 - October 13
At 800 million years ago, the Earth entered Epoch 4, with continuing increases in oxygen levels. This time period coincides with what is now known as the "Cambrian Explosion." Beginning 550 to 500 million years ago, the Cambrian Period is a significant marker post in the history of life on Earth: It is the time most major animal groups first appear in the fossil records. The Earth was now covered with swamps, seas and a few active volcanoes. The oceans were teaming with life.

EPOCH 5 - November 8
Finally, 300 million years ago in Epoch 5, life had moved from the oceans onto land. The Earth's atmosphere had reached its current composition of primarily nitrogen and oxygen. This was the beginning of the Mesozoic period that included the dinosaurs. The scenery looked like Jurassic Park on a Sunday afternoon.

EPOCH 6 - December 31 (11:59:59)
The intriguing question that remains is: What would Epoch 6, the time period humans occupy today, look like? Could we detect the telltale signs of alien technologies on distant worlds?
As the general consensus builds among scientist that human activity has altered Earth's atmosphere by inputting carbon dioxide as well as gases like Freon, could we identify the spectral fingerprints of those byproducts on other worlds? Although Earth-orbiting satellites and balloon experiments can measure these changes here at home, detecting similar effects on a distant world are beyond even the capabilities of upcoming programs like Terrestrial Planet Finder and Darwin. It will take gigantic flotillas of future space-based infrared telescopes to be able to accomplish those measurements.

"As daunting as this challenge sounds. I do believe in the next few decades we will know whether or not our little blue world is all alone in the Universe or if there are neighbours out there waiting to meet us" - Lisa Kaltenegger.

Source

Scientists have discovered an unusually large and light planet orbiting a star that could force them to re-examine theories about how planets are formed.

The planet, dubbed HAT-P-1, is roughly one-third larger than Jupiter but weighs only half as much, astronomers with the Harvard-Smithsonian Center for Astrophysics said Thursday.
The planet is about one-quarter the density of water.

"It’s lighter than a giant ball of cork" - Gaspar Bakos, Harvard-Smithsonian fellow .

HAT-P-1 revolves around its parent star once every 4.5 Earth days in an orbit one-seventh of the distance from Mercury to the sun.

Read more