Category: Extrasolar Planets

Astronomers have turned up plenty of extrasolar planets, but a newly discovered binary pair of planets is quite the find. The system consists of a 7-Jupiter mass planet and a 14-Jupiter mass planet… but no star. These planets – or “planemos” – just orbit each other. Their discovery challenges the current theory that planets are thought to form out of the disks of gas and dust that surround newborn stars.
Continue reading “Twin Planemos Discovered”

Nearly all of the extrasolar planets discovered so far have been huge, Jupiter-sized and above. The question is: could smaller, Earth-sized planets last in the same star systems? Researchers created a simulation where tiny planets were put into the same system as larger planets to see if they could gather enough material to become as large as the Earth. They found that one nearby system – 55 Cancri – could have formed terrestrial planets, with substantial water in the habitable zone.
Continue reading “Earth-Sized Planets Could Be Nearby”

New images of a relatively nearby protoplanetary disk, taken by the Subaru telescope on Mauna Kea, show strange banana-shaped arcs surrounding the central core. The most likely explanation for these arcs is that there’s another object orbiting the star; either a companion star or a large planet, and the gravitational interaction of this companion is distorting the disk of material. The protoplanetary disk, known as HT142527, is located 650 light-years away from Earth.
Continue reading “Protoplanetary Disk Warped by a Hidden Companion”

Astronomers from the University of St. Andrews have found evidence that a ring of dust around nearby Epsilon Eridani is rotating. The observations were made using the Submillimetre Common User Bolometer Array (SCUBA), which images the sky in the near infrared spectrum. This gives evidence to the theory that the disks of gas we see around newborn stars will eventually go on to become planets. In fact, the clumps of material tracked by the astronomers could even be newly forming planets themselves, still embedded in a vast disk of gas and dust.
Continue reading “Rotating Disk Could Contain Newly Forming Planets”

Correlation between the heavy elements in transiting planets and the metallicity of their parents. Image credit: A&A. Click to enlarge
Of the 188 extrasolar planets discovered, 10 are transits; we see them because they dim their parent star as they pass in front. This gives astronomers an opportunity to study the actual composition of these planets. European astronomers have discovered that the metal content of these “hot Jupiters” depends on the amount of metal in their parent star, which changes the size of their cores.

A team of European astronomers, led by T. Guillot (CNRS, Observatoire de la Cote d’Azur, France), will publish a new study of the physics of Pegasids (also known as hot Jupiters) in Astronomy & Astrophysics. They found that the amount of heavy elements in Pegasids is correlated to the metallicity of their parent stars. This is a first step in understanding the physical nature of the extrasolar planets.

Up to now, astronomers have discovered 188 extrasolar planets, among which 10 are known as “transiting planets”. These planets pass between their star and us at each orbit. Given the current technical limitations, the only transiting planets that can be detected are giant planets orbiting close to their parent star known as “hot Jupiters” or Pegasids. The ten transiting planets known thus far have masses between 110 and 430 Earth masses (for comparison, Jupiter, with 318 Earth masses, is the most massive planet in our Solar System).

Although rare, transiting planets are the key to understanding planetary formation because they are the only ones for which both the mass and radius can be determined. In principle, the obtained mean density can constrain their global composition. However, translating a mean density into a global composition needs accurate models of the internal structure and evolution of planets. The situation is made difficult by our relatively poor knowledge of the behaviour of matter at high pressures (the pressure in the interiors of giant planets is more than a million times the atmospheric pressure on Earth). Of the nine transiting planets known up to April 2006, only the least massive one could have its global composition determined satisfactorily. It was shown to possess a massive core of heavy elements, about 70 times the mass of the Earth, with a 40 Earth-mass envelope of hydrogen and helium. Of the remaining eight planets, six were found to be mostly made up of hydrogen and helium, like Jupiter and Saturn, but their core mass could not be determined. The last two were found to be too large to be explained by simple models.

Considering them as an ensemble for the first time, and accounting for the anomalously large planets, Tristan Guillot and his team found that the nine transiting planets have homogeneous properties, with a core mass ranging from 0 (no core, or a small one) up to 100 times the mass of the Earth, and a surrounding envelope of hydrogen and helium. Some of the Pegasids should therefore contain larger amounts of heavy elements than expected. When comparing the mass of heavy elements in the Pegasids to the metallicity of the parent stars, they also found a correlation to exist, with planets born around stars that are as metal-rich as our Sun and that have small cores, while planets orbiting stars that contain two to three times more metals have much larger cores. Their results will be published in Astronomy & Astrophysics.

Planet formation models have failed to predict the large amounts of heavy elements found this way in many planets, so these results imply that they need revising. The correlation between stellar and planetary composition has to be confirmed by further discoveries of transiting planets, but this work is a first step in studying the physical nature of extrasolar planets and their formation. It would explain why transiting planets are so hard to find, to start with. Because most Pegasids have relatively large cores, they are smaller than expected and more difficult to detect in transit in front of their stars. In any case, this is very promising for the CNES space mission COROT to be launched in October, which should discover and lead to characterization of tens of transiting planets, including smaller planets and planets orbiting too far from their star to be detected from the ground.

What of the tenth transiting planet? XO-1b was announced very recently and is also found to be an anomalously large planet orbiting a star of solar metallicity. Models imply that it has a very small core, so that this new discovery strengthens the proposed stellar-planetary metallicity correlation.

Original Source: NASA Astrobiology

Artist’s Concept of Transiting Planet XO-1b. Image credit: NASA/ESA/STScI. Click to enlarge
Amateur astronomers have used inexpensive equipment to discover a Jupiter-sized planet orbiting a Sun-like star 600 light-years away. The team used the “transit method”, to watch how a star dims slightly as a planet passes in front. An automated telescope observed tens of thousands of bright stars, and then the team chose a few dozen promising candidates. The new planet, dubbed X0-1b is the 10th planet ever discovered using the transit method.

An international team of professional and amateur astronomers, using simple off-the-shelf equipment to trawl the skies for planets outside our solar system, has hauled in its first “catch.”

The astronomers discovered a Jupiter-sized planet orbiting a Sun-like star 600 light-years from Earth in the constellation Corona Borealis. The team, led by Peter McCullough of the Space Telescope Science Institute in Baltimore, Md., includes four amateur astronomers from North America and Europe.

Using modest telescopes to search for extrasolar planets allows for a productive collaboration between professional and amateur astronomers that could accelerate the planet quest.

“This discovery suggests that a fleet of modest telescopes and the help of amateur astronomers can search for transiting extrasolar planets many times faster than we are now,” McCullough said. The finding has been accepted for publication in the Astrophysical Journal.

McCullough deployed a relatively inexpensive telescope made from commercial equipment to scan the skies for extrasolar planets. Called the XO telescope, it consists of two 200-millimeter telephoto camera lenses and looks like a pair of binoculars. The telescope is on the summit of the Haleakala volcano, in Hawaii.

“To replicate the XO prototype telescope would cost $60,000,” McCullough explained. “We have spent far more than that on software, in particular on designing and operating the system and extracting this planet from the data.”

McCullough’s team found the planet, dubbed X0-1b, by noticing slight dips in the star’s light output when the planet passed in front of the star, called a transit. The light from the star, called XO-1, dips by approximately 2 percent when the planet XO-1b passes in front of it. The observation also revealed that X0-1b is in a tight four-day orbit around its parent star.

Although astronomers have detected more than 180 extrasolar planets, X0-1b is only the tenth planet discovered using the transit method. It is the second planet found using telephoto lenses. The first, dubbed TrES-1, was reported in 2004. The transit method allows astronomers to determine a planet’s mass and size. Astronomers use this information to deduce the planet’s characteristics, such as its density.

The team confirmed the planet’s existence by using the Harlan J. Smith Telescope and the Hobby-Eberly Telescope at the University of Texas’s McDonald Observatory to measure the slight wobble induced by the planet on its parent star. This so-called radial-velocity method allowed the team to calculate a precise mass for the planet, which is slightly less than that of Jupiter (about 0.9 Jupiter masses). The planet also is much larger than its mass would suggest. “Of the planets that pass in front of their stars, XO-1b is the most similar to Jupiter yet known, and the star XO-1 is the most similar to the Sun,” McCullough said, although he was quick to add, “but XO-1b is much, much closer to its star than Jupiter is to the Sun.”

The astronomer’s innovative technique of using relatively inexpensive telescopes to look for eclipsing planets favors finding planets orbiting close to their parent stars. The planet also must be large enough to produce a measurable dip in starlight.

The planet is the first discovered in McCullough’s three-year search for transiting extrasolar planets. The planet quest is underwritten by a grant from NASA’s Origins program.

McCullough’s planet-finding technique involves nightly sweeps of the sky using the XO telescope in Hawaii to note the brightness of the stars it encounters. A computer software program sifts through many thousands of stars every two months looking for tiny dips in the stars’ light, the signature of a possible planetary transit. The computer comes up with a few hundred possibilities. From those candidates, McCullough and his team select a few dozen promising leads. He passes these stars on to the four amateur astronomers to study the possible transits more carefully.

From September 2003 to September 2005, the XO telescope observed tens of thousands of bright stars. In that time, his team of amateur astronomers studied a few dozen promising candidate stars identified by McCullough and his team. The star X0-1 was pegged as a promising candidate in June 2005. The amateur astronomers observed it in June and July 2005, confirming that a planet-sized object was eclipsing the star. McCullough’s team then turned to the McDonald Observatory in Texas to obtain the object’s mass and verify it as a planet. He received the news of the telescope’s observation at 12:06 a.m. Feb. 16, 2006, from Chris Johns-Krull, a friend and colleague at Rice University.

“It was a wonderful feeling because the team had worked for three years to find this one planet,” McCullough explained. “The discovery represents a few bytes out of nearly a terabyte of data: It’s like trying to distill gold out of seawater.”

The discovery also has special familial significance for the astronomer. “My father’s mentor was Harlan J. Smith, the man whose ambition and hard work produced the telescope that we used to acquire the verifying data.”

McCullough believes the newly found planet is a perfect candidate for study by the Hubble and Spitzer space telescopes. Hubble can measure precisely the star’s distance and the planet’s size. Spitzer can actually see the infrared radiation from the planet. By timing the disappearance of the planet behind the star, Spitzer also can measure the “ellipticity,” or “out-of-roundness,” of the planet’s orbit. If the orbit is elliptical, then the varying gravitational force would result in extra heating of the planet, expanding its atmosphere and perhaps explaining why the object’s diameter seems especially large for a body of its calculated mass.

“By timing the planet’s passages across the star, both amateur and professional astronomers might be lucky enough to detect the presence of another planet in the XO-1 system by its gravitational tugs on XO-1b,” McCullough said. “It’s even possible that such a planet could be similar to Earth.”

Original Source: HubbleSite News Release