The origin of comet material formed at high temperatures

July 22, 2011
Effect of photophoresis on a particle in the primordial nebula: the particle moves in the direction opposite to the Sun due to the variation in pressure of the gas, which is heated on the “day” side and cooled on the “night” side. Radiation Gas molecules Rapid Hot Force Slow Cold. Credit: O. Mousis

Comets are icy bodies, yet they are made of materials formed at very high temperatures. Where do these materials come from? French researchers have now provided the physical explanation behind this phenomenon. They have demonstrated how these materials migrated from the hottest parts of the solar system to its outer regions before entering the composition of comets. Their results are published in the July 2011 issue of the journal Astronomy & Astrophysics.

On 15 January 2006, after an eight-year voyage, NASA's Stardust Mission (Discovery program) brought dust from Wild 2 back to Earth. Comets are formed at very low temperatures (around 50 Kelvin, i.e. -223 C). However, analyses have revealed that Comet Wild 2 is made of crystalline silicates and CAIs (Calcium-Aluminium-rich Inclusions). Considering that the synthesis of these minerals requires very (above 1 000 Kelvin or 727 C), how can this composition be explained?

A team from the Institut UTINAM1, in collaboration with researchers from the Institut de Physique de Rennes, the University of Duisburg-Essen (Germany) and the Laboratoire Astrophysique, Instrumentation et Modélisation, have provided the answer on the basis of a physical phenomenon called photophoresis. This force depends on two parameters: the intensity of solar radiation and gas pressure.

At the birth of the solar system, the comets were formed from the protoplanetary disk. Inside this disk, a mixture of solid grains ranging in size from a few microns to several centimeters was bathed in a dilute gas that let sunlight through. According to the researchers, photophoresis drove the particles towards the outer regions of the disk. Under the effect of solar radiation, one face of the grains was “hotter” than the other and the behavior of gas molecules on the surface of these grains was modified: on the “sunny” side, the gas molecules were more unstable and moved about more rapidly than on the “cold” side.

By causing a pressure difference, this imbalance moved the grains away from the Sun (see diagram below). Through digital simulations, the researchers have borne out this photophoresis phenomenon. They demonstrated that the grains of crystalline silicates formed in the inner, hot region of the protoplanetary disk near to the Sun migrated to its outer, cold region before playing a part in the formation of the comets. This novel physical explanation could account for the position of certain dust rings observed in protoplanetary disks and thus shed light on the conditions of planet formation.

Explore further: Stardust lands in London: scientists look to comet for vital clues about Solar System

More information: Photophoretic transport of hot minerals in the solar nebula - A. Moudens, et al. - Astronomy and Astrophysics, 531 July 2011

Related Stories

Stardust Findings May Alter View of Comet Formation

March 14, 2006

Samples from comet Wild 2 have surprised scientists, indicating the formation of at least some comets may have included materials ejected by the early sun to the far reaches of the solar system.

First measurement of the age of cometary material

February 25, 2010

( -- Though comets are thought to be some of the oldest, most primitive bodies in the solar system, new research on comet Wild 2 indicates that inner solar system material was transported to the comet-forming ...

Recommended for you

Researchers find a new way to weigh a star

October 5, 2015

Researchers from the University of Southampton have developed a new method for measuring the mass of pulsars – highly magnetised rotating neutron stars formed from the remains of massive stars after they explode into supernovae.

How to prepare for Mars? NASA consults Navy sub force

October 5, 2015

As NASA contemplates a manned voyage to Mars and the effects missions deeper into space could have on astronauts, it's tapping research from another outfit with experience sending people to the deep: the U.S. Navy submarine ...

NASA selects investigations for future key planetary mission

October 1, 2015

NASA has selected five science investigations for refinement during the next year as a first step in choosing one or two missions for flight opportunities as early as 2020. Three of those chosen have ties to NASA's Jet Propulsion ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.