Editor TLN
March 28 () –
Asteroids sharing orbits with the planet Neptune have been observed to exist in a broad spectrum of red, which implies the existence of two populations of asteroids in the region.
An international team observed 18 asteroids that shared Neptune’s orbit, known as Neptunian Trojans. They are between 50 and 100 km in size and lie at a distance of around 4.5 billion km from the Sun. Asteroids orbiting this far are faint and therefore challenging for astronomers to study. Before the new work, only about a dozen Neptunian Trojans had been studied, requiring the use of some of the largest telescopes on Earth.
The new data, presented in Monthly Notices of the Royal Astronomical Society: Letters, were collected over the course of two years using the WASP wide-field camera on the Palomar Observatory telescope in California, the GMOS cameras on the Gemini North and South telescopes in Hawaii and Chile, and the LRIS camera on the Keck Telescope in Hawaii.
Of the 18 Neptunian Trojans observed, several were much redder than most asteroids, and compared to other asteroids in this group observed in previous studies. The redder asteroids are expected to have formed much farther from the Sun; a population of these is known as the classic cold trans-Neptunian objects that lie beyond the orbit of Pluto, some 6 billion kilometers from the Sun. The newly observed Neptunian Trojans are also different from asteroids located in the orbit of Jupiter, They tend to have a more neutral color.
The red color of asteroids implies that they contain a higher proportion of more volatile ices such as ammonia and methanol ices. These are extremely sensitive to heat and can quickly turn into a gas if the temperature rises, so they are more stable at great distances from the Sun.
The location of asteroids at the same orbital distance as Neptune also implies that they are stable on time scales comparable to the age of the Solar System. They effectively act as a time capsule, Recording the initial conditions of the Solar System.
The presence of redder asteroids among the Neptunian Trojans suggests the existence of a transition zone between more neutral and reddish colored objects. Redder Neptunian asteroids may have formed beyond this transition boundary before being captured in Neptune’s orbit. The Neptunian Trojans would have been captured in the same orbit as the planet Neptune when the ice giant planet migrated from the inner solar system to where it is now, some 4.5 billion kilometers from the Sun.
Lead author Dr. Bryce Bolin, of NASA’s Goddard Space Flight Center, said it’s a statement: “In our new work, we have more than doubled the sample of Neptunian Trojans studied with large telescopes. It is exciting to find the first evidence of redder asteroids in this group.”
“Because we have a larger sample of Neptunian Trojans with measured colors, we can now start to see important differences between asteroid groups. Our observations also show that Neptunian Trojans also have a different color compared to asteroid groups that are even further from the Sun. One possible explanation may be that the processing of asteroid surfaces by the Sun’s heat may have different effects for asteroids at different solar distances.”
