Solar Chemistry a New Key to Finding Exoplanets

12 11 2009

For many years researchers have pondered why our Sun has a negligible amount of lithium compared to other stars in our galaxy. In comparison, our Sun actually has less than 1% of the lithium present in most other stars. Researchers using the ESO’s HARPS spectrograph analyzed over 500 different stars, 70 of which are planet-bearing star systems and compared each one’s lithium content, as well as other light chemicals (in comparison to the atomic weight of iron). It was revealed that star systems which bear planets contain far less lithium than those systems which bear no planets.

Artist's impression of a baby star still surrounded by proto-planetary material in which planets could form.
Artist’s impression of a baby star still surrounded by proto-planetary material in which planets could form.

Somehow, it seems that systems which host planets provide a way to destroy the lithium over the years. Lithium is thought to have been an abundant element since the big bang and is present in most every star. The anomaly of chemical amounts that vary from star to star has bewildered researchers for over 60 years. So can planets and other planetary bodies affect the star in a way enough to destroy and realign chemical composition within that star? It seems that way. Theoreticians have their work cut out for them trying to figure out what causes the anomaly.

Researchers have undergone this project of measuring and analyzing lithium content in hopes of finding a way to detect star systems which bear planets in a way easier and faster than the current method using the HARPS device. For reference, HARPS is a device attached to the La Silla 3.6″ ESO telescope and studies the “wobble” of gravity and light from stars to detect if the star hosts a planet. If the current research is right, researchers may now use the HARPS device to detect lithium content from a star to determine the likelihood of the said star hosting planets.

The team of astronomers and researchers primarily involved in the project are: Garik Israelian, Elisa Delgado Mena, Carolina Domínguez Cerdeña, and Rafael Rebolo (Instituto de Astrofisíca de Canarias, La Laguna, Tenerife, Spain), Nuno Santos and Sergio Sousa (Centro de Astrofisica, Universidade de Porto, Portugal), Michel Mayor and Stéphane Udry (Observatoire de Genève, Switzerland), and Sofia Randich (INAF, Osservatorio di Arcetri, Firenze, Italy).

Journal Reference: G. Israelian et al. Enhanced lithium depletion in Sun-like stars with orbiting planets. Nature, November 12, 2009. Adapted from materials provided by ESO.


Two Jupiters That Shouldn’t Be – Retrograded and Tidally Ignorant

27 08 2009

WASP – The “Wide Area Search (for) Planets” is collaboration between various UK universities. Among modern collaborations, it is fit that it has become one of the most successful. Recent findings in the WASP program shine light on anti-fundamental understanding on astrophysics, planetary tidal effects and more. I’ll cast a little light on two of the discoveries by the program in this blog post.

An artist's impression of a transisting exoplanet.
An artist’s impression of a transiting exoplanet. (Credit: NASA/Hubble)

The first is the discovery of WASP-17 – a superhot gas-giant orbiting a star approximately 1,000 light years away. It was just another discovery of an extrasolar gas-giant, one of several found by the program until it was discovered that the planet had a strange behavior – a very strange behavior. It was found that WASP-17 actually orbited its star in reverse; it orbited in the opposite direction it was ‘supposed’ to orbit. It is well known that early star formations and young galaxies are very violent places – planetary collisions, streaming hot waves of gas and radiation and a hungry and devouring star at its center. When stars form, their planets form spinning and orbiting the same direction as the star when it formed…or so we thought. The star (and galaxy) rotates one way while WASP-17 rotates the other. No one really knows why or how this happened – it’s the first retrograde-orbiting planet discovered, but there’s a good guess looming out there.

Artist's impression shows a gas-giant exoplanet transisting across the face of a star.
Artist’s impression shows a gas-giant exoplanet transiting across the face of its star. (Credit: ESA/C. Carreau)

As mentioned, young galaxies and stars are quite violent – it is thought that perhaps early in WASP-17’s life, it collided with another, larger planet orbiting the same star. This collision flung WASP-17 the other way, causing its retrograde orbit. Collisions of this kind are quite common in this type of scenario – it’s actually the way our moon was formed – a mars-sized planetary body collided with earth sending massive clouds of dust and debris into space which eventually synthesized into what we call the moon.
Another interesting discovery of the WASP project was their next discover, WASP-18. WASP-18 was discovered by luck and chance, only being about a one in a thousand chance of being discovered^. The situation with WASP-18 is it is a planet with a mass ten times that of Jupiter but circles it’s star in less than one earth day. One Earth Day. Not only is its orbit as fast as is described, but its distance from its star is only about three stellar radii. That’s close. No one can quite figure out why the planet hasn’t already spiraled inward to its devouring doom within its parent star. According to what we know about planetary tidal forces and the gravity of bodies the size of the planet and its star, the planet should have been destroyed over a million years ago but yet it’s still spinning, orbiting the star. The only explanation for the scenario is that a) the tidal dissipation for that particular solar system is a thousand times less than that of our solar system or b) Our understanding of physics and tidal forces are limited to the scope of our own solar system – that things ‘out there’ are much, much different.

Science and Technology Facilities Council (2009, August 28). Huge New Planet Orbits ‘Wrong’ Way Around Star; Tells Of Game Of Planetary Billiards. ScienceDaily. Retrieved August 27, 2009, from /releases/2009/08/090827134159.htm
Nature (2009, August 27). Extrasolar Hot Jupiter: The Planet That ‘Shouldn’t Exist’. ScienceDaily. Retrieved August 27, 2009, from /releases/2009/08/090827132901.htm