Astronomers use ultra-sensitive camera to measure size of planet orbiting star

Dec 11, 2008
When the planet WASP-10b crosses the disk of its star, WASP-10, the brightness of the star decreases, allowing scientists to measure the precise size of the planet. Credit: Institute for Astronomy, University of Hawaii at Manoa

A team of astronomers led by John Johnson of the University of Hawaii's Institute for Astronomy has used a new technique to measure the precise size of a planet around a distant star. They used a camera so sensitive that it could detect the passage of a moth in front of a lit window from a distance of 1,000 miles.

The camera, mounted on the UH 2.2-meter telescope on Mauna Kea, measures the small decrease in brightness that occurs when a planet passes in front of its star along the line-of-sight from Earth. These "planet transits" allow researchers to measure the diameters of worlds outside our solar system.

"While we know of more than 330 planets orbiting other stars in our Milky Way galaxy, we can measure the physical sizes of only the few that line up just right to transit," explains Johnson. The team studied a planet called WASP-10b, which was thought to have an unusually large diameter. They were able to measure its diameter with much higher precision than before, leading to the finding that it is one of the densest planets known, rather than one of the most bloated. The planet orbits the star WASP-10, which is about 300 light-years from Earth.

IfA astronomer John Tonry designed the camera, known as OPTIC (Orthogonal Parallel Transfer Imaging Camera), and it was built at the IfA. It uses a new type of detector, an orthogonal transfer array, the same type used in the Pan-STARRS 1.4 Gigapixel Camera, the largest digital camera in the world. These detectors are similar to the CCDs (charge-coupled devices) commonly used in scientific and consumer digital cameras, but they are more stable and can collect more light, which leads to higher precision.

"This new detector design is really going to change the way we study planets. It's the killer app for planet transits," said team member Joshua Winn of MIT. The precision of the camera is high enough to detect transits of much smaller planets than previously possible. It measures light to a precision of one part in 2,000. For the first time, scientists are approaching the precision needed to measure transits of Earth-size planets.

Bigger planets block more of the star's surface and cause a deeper brightness dip. The diameter of WASP-10b is only 6 percent larger than that of Jupiter, even though WASP-10b is three times more massive. Correspondingly, its density is about three times higher than Jupiter's. Because their interiors become partially degenerate, Jovian planets have a nearly constant radius across a wide range of masses.

The photometric precision is three to four times higher than that of typical CCDs and two to three times higher than the best CCDs, and comparable to the most recent results from the Hubble Space Telescope for stars of the same brightness.

The scientific paper presenting this discovery will be published in the Astrophysical Journal Letters. A preprint is available on the Web at arxiv.org/abs/0812.0029 .

Source: University of Hawaii at Manoa

Explore further: Can astronomy explain the biblical Star of Bethlehem?

add to favorites email to friend print save as pdf

Related Stories

Video: Flying over Becquerel

Dec 19, 2014

This latest release from the camera on ESA's Mars Express is a simulated flight over the Becquerel crater, showing large-scale deposits of sedimentary material.

Bright lights: big cities at night

Dec 17, 2014

As the days grow shorter and the temperatures drop in Europe, test your geography skills in the warmth of your home – while helping scientists to pinpoint light pollution.

Mars mission boost welcomed by scientists

Dec 15, 2014

University of Leicester scientists, who are closely involved in the European mission to Mars –ExoMars- have welcomed support from the Government for the project.

Image: Jupiter's bands of bronze

Dec 08, 2014

This Cassini image shows Jupiter from an unusual perspective. If you were to float just beneath the giant planet and look directly up, you would be greeted with this striking sight: red, bronze and white ...

Recommended for you

Can astronomy explain the biblical Star of Bethlehem?

Dec 24, 2014

Bright stars top Christmas trees in Christian homes around much of the world. The faithful sing about the Star of Wonder that guided the wise men to a manger in the little town of Bethlehem, where Jesus was ...

Hubbles spies the beautiful galaxy IC 335

Dec 24, 2014

This new NASA/ESA Hubble Space Telescope image shows the galaxy IC 335 in front of a backdrop of distant galaxies. IC 335 is part of a galaxy group containing three other galaxies, and located in the Fornax ...

Image: Multicoloured view of supernova remnant

Dec 22, 2014

Most celestial events unfold over thousands of years or more, making it impossible to follow their evolution on human timescales. Supernovas are notable exceptions, the powerful stellar explosions that make ...

Ultra-luminous X-ray sources in starburst galaxies

Dec 22, 2014

Ultra-luminous X-ray sources (ULXs) are point sources in the sky that are so bright in X-rays that each emits more radiation than a million suns emit at all wavelengths. ULXs are rare. Most galaxies (including ...

When a bright light fades

Dec 22, 2014

Astronomer Charles Telesco is primarily interested in the creation of planets and stars. So, when the University of Florida's giant telescope was pointed at a star undergoing a magnificent and explosive death, ...

User comments : 4

Adjust slider to filter visible comments by rank

Display comments: newest first

Hoarsesenz
1.3 / 5 (3) Dec 11, 2008
Event 1: An earth size planet is discovered with water in the atmosphere.

Event 2 (later that same year): US and ESA and Chinese and Japanese and Russian space program funding is increased by an order of magnitude.
theophys
2.3 / 5 (3) Dec 12, 2008
Event 1: An earth size planet is discovered with water in the atmosphere.

Event 2 (later that same year): US and ESA and Chinese and Japanese and Russian space program funding is increased by an order of magnitude.

Yay for funding!
Thecis
1 / 5 (1) Dec 12, 2008
This could be a possibility.
Yet, it might be some time before that. The planets found until now are about the size of Jupiter! the diameter of earth is roughly 11 times smaller. The way we would see such a planet is 11^2 = 121 times smaller!
It would take a much more senstive camera to be able to see that one.
Not to mention the following situation: what happens if a earth like planet AND a jupiter like planet would go in front of a star? How would we know the measurement would be influenced by a planet that is 120 times smaller. At this moment the fluctuation would be considered as noise and not taken into account.
Like I stated earlier. It will be possible but with a much more sensitive camera. After that, it might be possible to detect water etc. with spectroscopic techniques that will be improved also at that time.
When that has happened I also hope that space programs will be funded more than they are now. And I hope they will work together as well...
denijane
2.5 / 5 (2) Dec 15, 2008
I'm not entirely sure, however, where ESA or NASA would get the money from, even if they discover such planet tomorrow. So, I think this research is more a marvellous example of what we can do with what we have, than just a publicity stunt aiming at the money.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.