SCIENCE: Important Clue Toward Finding Life on Other Planets

By Tito Drago Reprint | | Print |

Tito Drago

MADRID, May 9 2001 (IPS) - The discovery that a planet was probably consumed by its star marks a big step toward understanding planetary systems in general, and the possibility of one day finding other inhabited planets, Armenian scientist Garik Israelian told IPS.

Israelian and his Spanish colleague Rafael Rebolo are the authors of an article appearing in this Thursday’s edition of the scientific journal Nature in which the two experts present evidence that the planetary system surrounding star HD 82943, with at least two giant Jupiter-like planets, had at least one more planet, but which was absorbed by the star.

Star HD 82943 is similar to our Sun and forms part of the Hydra constellation.

The verification of this possible event was carried out jointly by the Astrophysics Institute of the Canary Islands (IAC) in Spain, where Israelian and Rebolo work, and the Geneva Observatory, based on data obtained by the European Southern Observatory on Cerro Paranal, in northern Chile, considered the best observatory in the world.

The information provided by the extremely advanced telescopes at Paranal has meant major steps forward in the last few years in the detection and analysis of planetary systems, crucial for determining whether there exist others like our solar system, said Israelian.

So far, astrophysicists have not detected a system similar to ours, with its nine planets orbiting the Sun, because the available technologies do not allow it, “but there could be others, and many of them, which is why this research is so important,” he added.

Observations conducted during the last six years indicate that gigantic planets, like Jupiter, can be found orbiting at least 60 stars, some of which are the centre of systems comprising more than one planet, in many cases with orbits as close to the star as Mercury is to the Sun.

However, experts are still unable to explain the existence of gigantic planets so close to their stars. The latest theories on planetary systems maintain that such planets can only originate at much greater distances from the system’s centre.

The most recent discoveries suggest that giant planets could have been pushed from their original orbits to other paths closer to their stars as a result of consequences that are still not fully understood.

Israelian, Rebolo and their counterparts at the Geneva Observatory, Nuno Santos and Michel Mayor, discovered that star HD 82943 has a high content of the lithium-6 isotope.

This lithium isotope does not exist in stars that are similar to the Sun in age and chemical composition because the quantity of lithium-6 present when the star is formed is quickly destroyed by internal nuclear reactions during the first stages of stellar evolution.

Lithium-6 is preserved, however, in giant planets and in what are known as “brown dwarfs,” celestial objects of great mass that do not become stars because they do not reach the high temperatures necessary to sustain nuclear fusion at their core.

The research conducted by the IAC and the Geneva Observatory is the first in which the presence of lithium isotopes was studied to determine possible planetary migrational phenomena, Rebolo pointed out.

The level of lithium-6 detected in HD 82943 is similar to that found in the meteorites of our solar system, suggesting that the existence of the isotope in the star is due to the fact that it absorbed one or more planets, he explained.

The phenomenon could have been produced by the interaction of the gravitational forces of the system’s planets, or the interaction of a planet with protoplanetary material like gases, dust or asteroids, added Rebolo.

A dynamic of this sort would have caused “a movement similar to that produced by the impact of billiard balls,” explained fellow researcher Israelian.

The data recorded on lithium isotopes allowed the physicists to establish that HD 82943 could have “devoured” a gaseous planet two or three times the mass of Jupiter and with a similar chemical make-up, or else a denser planet with a chemical composition like that of the solar system’s meteorites.

“It is the first time that such direct evidence has been discovered about this kind of phenomenon, though it has been said for years that some systems appear to have planets in orbits that cannot be stable, which could lead them to be hurled into the star or out of the system,” said Rebolo.

“The collision of a planet with HD 82943 would have been an impressive phenomenon. To give us an idea of it, we can imagine what the impact of the Shoemaker-Levy 9 comet colliding with Jupiter, and multiply the energy of the impact by a factor of at least 100 billion,” Israelian commented.

The star could have absorbed the planet within the last five billion years, added the Armenian-born scientist.

Our solar system is some 4.0 billion years old, according to the calculations of experts in the field of astrophysics.

“We would like to be able to study the chemical composition of other stars with planets and to construct a general theory to better understand the formation and evolution of all planetary systems, including our own,” Israelian said.

When asked if life might exist in other planetary systems, the physicist thought for a moment, smiled, and said: “Of course there could be life, and a lot of it.” But to find it, we must continue exploring the heavens.