Clear evidence of planet formation found in Pleiades

William Atkins
Sunday, 18 November 2007 20:14

Science - Space

Microsoft Office 365

Using the 8-meter Frederick C. Gillett Telescope at the Gemini Observatory in Hawaii (Gemini North), and the (current) NASA Spitzer Space Telescope and the (former) Infrared Astronomical Satellite (IRAS) orbiting observatories, U.S. astronomers have found observational evidence in the infrared portion of the electromagnetic radiation spectrum that rocky planets (terrestrial planets like Earth or Mars) are forming in the solar system.

They contend that the formation of terrestrial planets is very common based on the amount of dust that has formed as a result of collisions between rocky planets.

The Pleiades star cluster, also called the “Seven Sister” because of its nine brightest stars, is a group of about 1,400 stars within the constellation Taurus. The “seven sisters” stars are easily seen in the night sky: Sterope, Merope, Merope, Electra, Maia, Taygete, Celaeno, and Alcyone, and their parent stars Atlas and Pleione.

The results of the astronomical researchers—Joseph Rhee (UCLA), Inseok Song (NASA Spitzer Science Center at the California Institute of Technology), and Benjamin Zuckerman (UCLA)—will appear in an upcoming issue of the Astrophysical Journal.

Specifically, the researchers found the star HD 23514 contains a multitude of warm dust particles—hundreds of thousands of times more warm dust particles than what surrounds the Sun. Such an extraordinary amount of dust particles is thought to be the result of a gigantic collision of planets or protoplanets.

These hot dust particles can first form into comets and small asteroids, which can later form into protoplanets (small, early-stage bodies, about the size of moons, which may later develop into planets if given the right conditions). Under other conditions, these protoplanets collide and obliterate each other—forming huge numbers of warm dust particles.

The researchers contend that the dust particles found around HD 23514, which is about 100 million years old, are the result of protoplanets colliding and destroying each other. Based on data from HD 23514, along with the star BD +20 307 that is about 400 million years old, they contend that most Sun-like stars are likely involved in the formation of terrestrial-type planets as massive amounts of warm dust particles continually clump together and get bigger and bigger with time. Some of these clumps form protoplanets, and some of these protoplanets become full-fledged planets.

These two stars are prime examples of stars containing second-generation debris; that is, debris that has had enough time (tens of millions of years) to either clump together to form much larger objects or collide with each other to form massive amounts of dust. First-generation debris, or primordial dust, is usually found around younger stars, less than ten millions years old, which have not had enough time to form into larger bodies.

The discovery by the Rhee team is very important in the developing theory on how planets are forming outside of our solar system, and how our eight planets (and several dwarf planets and other objects such as comets and asteroids) formed billions of years ago around the Sun.