European Space Agency probe to intercept a comet

European Space Agency probe to intercept a comet

Comet illustration

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Artwork: There may be little warning of a very distant visitor

The European Space Agency is to launch another mission to a comet.

After the hugely successful Rosetta encounter with the icy dirt-ball known as 67P/Churyumov-Gerasimenko in 2014, officials have now selected a new venture that will launch in 2028.

It’s called Comet Interceptor and will aim to catch and study an object that has come in towards the Sun from the outer reaches of the Solar System.

Scientifically, it will be led from the UK’s Mullard Space Science Laboratory.

The concept is a three-in-one probe: a mothership and two smaller daughter craft. They will separate near the comet to conduct different but complementary studies.

The cost for Esa is expected to be about €150m. As is customary, individual member states will provide the instrumentation and cover that tab.

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Rosetta spent two years at Comet 67P, taking thousands of photos

Interceptor was selected on Wednesday by the agency’s Science Programme Committee as part of the new F-Class series – “F” standing for fast. The call for ideas only went out a year ago.

There will now be a period of feasibility assessment with industry before the committee reconvenes to formally “adopt” the concept. At that point, the mission becomes the real deal.

The intention is to launch the probe on the same rocket as Esa’s Ariel space telescope when it goes up at the end of the next decade. This observatory won’t use the full performance of its launch vehicle, and so spare mass and volume is available to do something additional.

And it’s Ariel’s destination that makes Interceptor a compelling prospect.

The telescope is to be positioned at a “gravitational sweetspot” about 1.5 million km from Earth. This is an ideal position from which to study distant stars and their planets – but it also represents a fast-response “parking bay” for any new mission seeking a target of opportunity.

The type of comets being sought by Interceptor tend to give little notice of their arrival in the inner Solar System – perhaps only a few months.

That’s insufficient time to plan, build and launch a spacecraft. You need to be out there already, waiting for the call.

This is what Interceptor will do. It will be sitting at the sweetspot, relying on sky surveys to find it a suitable target. When that object is identified, the probe will then set off to meet it.

The encounter will be very different from that of Rosetta at 67P. Interceptor will not orbit the comet; it will just fly past – hopefully not to quickly.

Nor will Interceptor try to repeat the landing of Rosetta’s little robot, Philae.

Instead, it will be the job of those daughter craft to see if they can get in a bit closer to the comet than the mothership to acquire some more detailed information.

All the comets visited so far by space probes have been “short period” objects. That is, they move back and forth between the Sun and the orbit of the planet Jupiter.

Many have gone close to our star on multiple occasions, and that means they’ve been chemically altered by heat, particle radiation and even numerous impacts with other bodies.

In contrast, the comets that come in from the so-called Oort Cloud – a band of icy material that resides several hundred billion km from the Sun – will be pristine. And to see one at close quarters should give scientists completely new insights into the conditions that existed at the inception of the Solar System, and potentially from even further back in time.

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