London, Jan 16 : Astronomers have used new radar observations to suggest that a peanut shaped comet might have formed when two comets collided and stuck together.
For observing the comet 8P/Tuttle, as it is referred to, astronomers used the Arecibo telescope in Puerto Rico, which gave them a detailed and surprising view of the comet's nucleus, which resembled a peanut.
According to a report in New Scientist, Arecibo's unique planetary radar was able to resolve the comet's shape to within 300 metres and found that the comet's main body was made up of two spheres - spanning 3 and 4 km.
"We clearly see it looking like two balls," Arecibo's Mike Nolan told New Scientist.
From three nights of observations, astronomers estimate that the double nucleus rotates once in 7.7 hours, while the comet orbits the Sun every 13.6 years.
According to the report, it is the first comet ever found that appears to be a so-called "contact binary", though several peanut-shaped asteroids may have formed in low-speed collisions between other space rocks.
But astronomers are puzzled that how can a contact binary could form in this case, since its two component parts would have to be moving relatively slowly with respect to each other to actually stick together.
One possibility is that the binary was originally a single comet that got pulled apart by the gravitational pull of a large planet or the Sun - a relatively easy feat since comets are like fluffy snowballs and therefore lack internal strength.
"The gravitational tug could cause a comet to stretch so much that it actually splits in the middle, making two little mini-globes that fall back together," said Derek Richardson of the University of Maryland in College Park, US.
"A comet could also come apart if it rotated too fast on its axis, although that is unlikely given Tuttle's slow rotation rate," he added.
"Low-speed collisions in the early solar system are another possibility," said Dan Scheeres of the University of Colorado in Boulder, US. "Such events seem unlikely given that most objects should be moving too quickly to bond together, but if they do form, contact binaries can be stable for very long time spans," he added.