Tailless 'Manx' comet provides window to Earth's formation

Friday, April 29, 2016, 3:53 PM -

A unique tailless "Manx" comet is giving astronomers a glimpse at a preserved fragment from a time when Earth was just forming. The hunt is now on for more of these objects, to provide us with clues about the origin of our planet and our solar system.

In September of 2014, astronomers spotted a new object swinging through the inner solar system. Dubbed with the rather unremarkable name of C/2014 S3 (PANSTARRS), this object had the distinct orbit of a comet - a roughly 860-year elliptical path around the Sun that takes it from just beyond the orbit of Mars, out to the Oort cloud at the edge of the solar system and back - however it was far too faint to be an ordinary example of these icy wanderers.

To discover the true nature of C/2014 S3, a team trained the strongest ground-based telescope on it that we have - the appropriately named Very Large Telescope (VLT), located at the European Southern Observatory (ESO), in northern Chile. 

What they found was a rocky object, like any stony asteroid you'd find in the asteroid belt between Mars and Jupiter, with just a hint of water vapour around it, forming a faint, very tiny tail. Based on this, the astronomers called this a "Manx" comet, after the tailless cats. While there have been other asteroid-like "rock comets" discovered, the light scattering off of this one revealed it to be something unique.

"What makes this object, S3, really special is its nature," ESO astronomer and study co-author Olivier Hainaut wrote in an email to The Weather Network. "Our observations show that it is rocky, while normal Oort cloud comets are almost entirely composed of dirty ice. This indicates S3 has formed in the inner solar system."

"Also, the spectrum of the rock, the detailed analysis of how it reflects light at different colours, indicate it is very primitive and unprocessed, with tiny traces of water, which confirms that it was ejected from a very, very young inner solar system - when and where the Earth was forming," Hainaut explained.

This is quite an exciting find, because it is the first time astronomers have ever seen anything like it - a pristine fragment of the early inner solar system. Preserved by the freezing temperatures of the distant edges of the solar system, it has only recently returned to our region of space, to within viewing distance of those who can study it.

"We already knew of many asteroids, but they have all been baked by billions of years near the Sun," astronomer Karen Meech, the lead author of the study from the University of Hawaii, said in an ESO statement. "This one is the first uncooked asteroid we could observe: it has been preserved in the best freezer there is."

C/2014 S3's plummet from the edge of the solar system towards the Sun, and then settling into its new orbit. Credit: ESO/L. Calçada/S. Sutherland

First pass?

Although 2014 was the first time C/2014 S3 was spotted, it's unlikely that this was the first pass it has made through the inner solar system since its initial ejection.

"From its current orbit, we know that S3 comes from the Oort cloud, but we also know that it is not its first passage," said Hainaut. "The orbit bears the mark of interactions with Jupiter (possibly Saturn, possibly both), so it must have passed a few times before."

According to Hainaut, even a few dozen, or a hundred orbits would still leave its surface relatively untouched compared to similar objects in the asteroid belt, which have made millions to billions of orbits since the solar system formed.

Hints at our origins

Although studies of comets in the past have tried to provide answers to the origin of Earth's water, C/2014 S3, along with its thin water vapour halo, was far too faint to produce any meaningful information for that purpose.

Based on this study, though, the properties of S3 provide a glimpse at something more fundamental: what many of the "building blocks" of the rocky planets - Mercury, Venus, Earth and Mars - would have been like back in the early days of the solar system. This information, along with an idea of the fraction of the Oort cloud that's made up of these Manx comets, could give astronomers enough clues to narrow down the field of models currently competing to describe exactly how the solar system formed and evolved.

"We’ve found the first rocky comet, and we are looking for others," Hainaut said in the ESO press release. "Depending how many we find, we will know whether the giant planets danced across the Solar System when they were young, or if they grew up quietly without moving much."

Source: ESO

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