An artist's impression of a Hot Jupiter passing in front of its star ... dimming of starlight in this case was used to detect the two new planets.
Credit: University of Florida
GAINESVILLE, Florida: Astronomers have discovered two new planets outside our Solar System, both extremely close to their stars and thus among the hottest ever found.
"We can expect these two planets to be the first in a wave of a whole lot of these new types of planets," said Stephen Kane of the University of Florida, one of more than three dozen scientists involved in the discovery. The two new additions were announced this week at the Transiting Extrasolar Planets Workshop at the Max Planck Institute for Astronomy in Heidelberg, Germany.
Known as "Hot Jupiters" because of their Jupiter-like size, but higher temperature, the new planets are so close to their stars that they complete their orbit in a mere two and two-and-a-half days, respectively. That compares to 88 days for Mercury, the planet with the fastest orbit in our Solar System.
The very close orbit also means that the new planets are hotter than Mercury, which has a surface temperature of 400 degrees Celsius. The planets are estimated to have a temperature of at least 1,800 degrees.
There is also evidence that the solar radiation from the stars is so intense that it is whipping away their atmospheres. "Hot Jupiters are assumed to have a significantly reduced lifetime due to their proximity to the star," said Kane.
Most planets outside our Solar System have been found using a technique called the radial velocity method, which measures the gravitational wobble in a star induced by the orbiting planet. In this case, the astronomers found the planets by detecting the slight dimming of starlight that occurs when planets pass in front of their stars.
Of about 200 planets discovered so far, these are only the 13th and 14th to be found using this technique, called the transit method. According to Kane, that number is set to rise as a U.K.-based effort to discover planets with the transit method gathers steam.
At first glance, the transit method seems impractical because it requires a lucky break: the orbital plane of a planet must be aligned toward Earth so that astronomers can see the starlight dim as the planet passes by. However the astronomers who found these two new planets overcame this problem with "brute force", said Kane.
They surveyed millions of stars using twin telescopes, snapping photos of the southern and northern skies from two locations: La Palma in Spain's Canary Islands and Sutherland in South Africa. Each telescope is equipped with eight wide-angle cameras, each of which has a field of view of eight degrees, which comprises a relatively large chunk of the sky. By comparison, the full moon comprises about half a degree.
The work was done through the U.K.'s leading planet detection program, a consortium of eight universities called SuperWASP, or Wide Angle Search for Planets.
Kane's role in the research was to help pick out from the vast numbers of photographed stars the most likely candidates for further investigation. The job was a difficult one because planets passing in front of stars only slightly diminish the starlight, dimming it by only about one per cent for just a few hours.
"We have computer programs which are able to search all of these light curves from the stars and see if there's something in them which looks like the star has become fainter for a short period, but it's a complicated task," Kane said.
After SuperWASP identified the tiny dips in starlight caused when the planets passed in front of their stars, a French-built instrument detected a slight wobble in each star's motion as the planets passed around them, confirming the existence of the planets.
The planets are located in the constellations Andromeda and Delphinius, respectively. The Andromeda planet is more than 1,000 light years away, while the Delphinius planet is 500 light years away.
Both of the new planets are far too hot to support life. But Kane said their discovery adds to growing knowledge about how planets form, which should help astronomers understand and zero in on Earth-like planets.
"Once we understand planet formation, we'll understand a lot more about how terrestrial planets form as well," he said.
with the University of Florida
They're so hot right now
How many planets are we going to find? Seems the more we look the more we find. It's incredible!
planets
the more we look the more we find. By the way when did they were found
I love it!
If we keep this up, our eight planets will be our twenty-nine planets.