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Scientists obtain detailed information into the heart of two planetary systems

By probing regions of a similar scale to Earth's orbit, scientists can observe the dusty results of massive collisions in the final stages of rocky planet formation and learn about the conditions earthlike planets in other planetary systems may experience.
Provided by the Royal Astronomical Society, United Kingdom
MIDI interferometer HD 69830 results
Scientists observed the star HD 69830 in the mid-infrared on a single 8-meter telescope. This image looks the same as the image of a star with no dust around it.
ESO/Rachel Smith
April 16, 2010
Using four of the world's largest telescopes, scientists have obtained the most detailed information yet from the regions around two young stars tens of light-years away, finding compact disks of rocky and dusty material at distances comparable to that from Earth to the Sun. Keele University astronomer Rachel Smith presented the team's results Wednesday, April 14 at the Royal Astronomical Society's National Astronomy Meeting in Glasgow.

The astronomers used data from the MIDI interferometer, an instrument that combines the infrared light from the 8-meter diameter telescopes of the European Southern Observatory's Very Large Telescope in Chile to simulate the performance of a single telescope with a mirror more than 330 feet (100 meters) across.
MIDI interferometer HD 69830 results
Researchers compared a star with no dust around it with HD 69830 to confirm they didn't not see extended dust emission with a single telescope.
ESO/Rachel Smith
Two of the stars observed with MIDI are similar to our Sun — one is a little cooler and one a little hotter. The first, cataloged as HD 69830, is an orange star with spectral type K0V and is thought to be about 2 billion years old (compared with the Sun's age of 4.5 billion years). It lies in the direction of the southern constellation Puppis, is around 41 light-years from the Sun and is known to have three planets with masses comparable to Neptune. The second star, Eta Corvi (in the constellation Corvus and 59 light-years from the Sun) is spectral class F2V, equivalent to a yellow-white color, and is about 1.3 billion years old. Earlier observations hinted at disks of material around both stars. Scientists confirmed cold material around Eta Corvi, as it lies 14 billion miles (22.5 billion kilometers) from that star and so was easier to spot.
MIDI interferometer HD 69830 results
When the team of researchers subtracted the image of a normal star from the image of HD 69830, they could see clearly that they cannot resolve the dust emission with a single telescope.
ESO/Rachel Smith
With MIDI, the region of the relatively small dusty disk around HD 69830 is clear and lies between 4.7 and 224 million miles (7.5 and 360 million km) from the star. If you were standing on the surface of one of its planets, this dust would be a spectacular sight, several thousand times brighter than the similar but much fainter zodiacal dust that you can see from the Earth on a dark night.

One intriguing possibility for the source of the dust is that the planets around HD 69830 are experiencing a high rate of impacts from asteroids and comets smashing into their surfaces. A similar disk also exists close in to Eta Corvi, lying between 15 and 280 million miles (24 to 450 million km) from its stellar host. For comparison, Earth is on average about 93 million miles (150 million km) away from the Sun.
MIDI interferometer HD 69830 results
When the scientists combined the light from two 8-meters telescopes with MIDI, they could simulate the resolving power of a telescope with a diameter of about 100 meters. These observations gave a "visibility function," which measures how resolved a source is: A visibility of 1 happens when a source is completely unresolved while lower visibilities indicate increased resolution. For HD 69830, the scientists did not resolve the star itself, but did resolve the dust emission, as the visibility clearly does not match the pattern of an unresolved source (dashed blue line). The levels of dust emission vary in the wavelength range covered in the observation (8-13 microns, a region of the mid-infrared spectral range), and this variation can also be seen in the visibility function. These results show that the dust lies between 4.7 and 224 million miles (7.5 and 360 million km) from the star (0.05 to 3 times the Earth-Sun distance).
ESO/Rachel Smith
These results represent the first resolution of dusty disks so close in to their parent stars with observations made possible using an interferometer like MIDI. The ages of the two stars and the locations of the dusty disks suggests that they may either originate from the debris of recent collisions of massive objects or travel there from an outer, cooler disk like the one around Eta Corvi.

Smith sees this work as part of the overall quest to find earthlike planets around other stars. "With MIDI, we have access to a truly giant telescope that can see the universe in unprecedented detail," she said. "By probing regions of a similar scale to the Earth's orbit, we have the potential to observe the dusty results of massive collisions in the final stages of rocky planet formation and learn about the conditions earthlike planets in other planetary systems may experience. The opportunities for directly testing our theories for how planets form and evolve have never been greater."
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