Science

NASA planet-hunting satellite captures comet spewing 1,000,000 KG of material


NASA’s Transiting Exoplanet Survey Satellite (TESS) recorded the moment ice and dust vaporised from comet 46P/Wirtanen in 2018 as it made a close Earth approach. The explosion lasted for 20 days and ejected one million kg (2.2million pounds) of material – and NASA used a series of images to create a timelapse of the extremely rare event.

Wirtanen was first spotted orbiting the Sun in the 1940s and last year the comet it came within 30 times the distance to the Moon.

Wirtanen’s explosion occurred on September 26, 2018 and occurred in two phases.

There was an hour-long explosion followed by a steadier second stage that gradually grew brighter over the succeeding eight hours after the in initial outburst.

The researchers believe the second stage was a consequence of spreading comet dust reflecting more sunlight.

Once the comet reached peak brightness, Wirtanen began to fade over a period of two weeks, meaning the explosion lasted for approximately 20 days.

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Dr Tony Farnham, a research scientist in the UMD Department of Astronomy and the lead author of the research paper, said: “With 20 days’ worth of very frequent images, we were able to assess changes in brightness very easily.

“That’s what TESS was designed for, to perform its primary job as an exoplanet surveyor.

“We can’t predict when comet outbursts will happen. But even if we somehow had the opportunity to schedule these observations, we couldn’t have done any better in terms of timing.

“The outburst happened mere days after the observations started.”

The scientists estimate a total of 1million kilograms of ice and dust was ejected from the burst.

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Dr Farnham added: “TESS spends nearly a month at a time imaging one portion of the sky.

“With no day or night breaks and no atmospheric interference, we have a very uniform, long-duration set of observations.

“As comets orbit the Sun, they can pass through TESS’ field of view.

“Wirtanen was a high priority for us because of its close approach in late 2018, so we decided to use its appearance in the TESS images as a test case to see what we could get out of it.

“We did so and were very surprised!”

The most common comet activity occurs when sunlight vaporises the ice near the surface of the nucleus, and the outflowing gases drag dust off the nucleus to form the coma.

However, comets are also known to experience occasional spontaneous outbursts capable of significantly increase the comet’s activity.

It is not currently known the cause of these comet outbursts, but they are related to the conditions on their surfaces.

The researchers offered suggestions for what might have occurred, including a thermal event, where a heat wave penetrates into a pocket of highly volatile ices, causing the ice to rapidly vaporise and produce an explosion of activity.

Others suggest a chemical event was responsible, where a cliff collapses, exposing fresh ice to direct sunlight.

NASA said in a statement: “Studies of the outburst behaviour, especially in the early brightening stages that are difficult to capture, can help us understand the physical and thermal properties of the comet.”

TESS has also detected Comet Wirtanen’s dust trail for the first time.

Unlike a comet’s tail — the spray of gas and fine dust that follows behind a comet, growing as it approaches the sun — a comet’s trail is a field of larger debris that traces the comet’s orbital path as it hurtles around the Sun.

Unlike a tail, which changes direction as it is blown by the solar wind, the orientation of the trail stays more or less constant over time.

Dr Michael Kelley, an associate research scientist in the UMD Department of Astronomy and a co-author of the research paper, said: “The trail more closely follows the orbit of the comet, while the tail is offset from it, as it gets pushed around by the sun’s radiation pressure.

“What’s significant about the trail is that it contains the largest material.

“Tail dust is very fine, a lot like smoke. But trail dust is much larger—more like sand and pebbles.

“We think comets lose most of their mass through their dust trails. When the Earth runs into a comet’s dust trail, we get meteor showers.”



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