Science

NASA's planet-hunting satellite captures massive spontaneous outburst of a comet


NASA‘s exoplanet-hunting satellite captured the most complete and detailed observation of a comet’s spontaneous outburst in history.

The Transiting Exoplanet Survey Satellite (TESS) recorded the moment ice and dust exploded from the comet 46P/Wirtanen in 2018 as it made its closest pass to Earth.

The burst lasted for 20 days and ejected 2.2 million pounds of material- and NASA used a series of images to create a timelapse of the rare event.

Wirtanen was first spotted orbiting the sun in the 1940s, but last year it it came within 30 times the distance to the moon.

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

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NASA's exoplanet-hunting satellite captured the most complete and detailed observation of a comet's spontaneous outburst in history. The Transiting Exoplanet Survey Satellite (TESS) recorded the moment ice and dust exploded from the comet 46P/Wirtanen in 2018 as it made its closest pass to Earth

NASA’s exoplanet-hunting satellite captured the most complete and detailed observation of a comet’s spontaneous outburst in history. The Transiting Exoplanet Survey Satellite (TESS) recorded the moment ice and dust exploded from the comet 46P/Wirtanen in 2018 as it made its closest pass to Earth

There was an hour-long flash followed by a more steady second stage that gradually become brighter over the next eight hours after the outburst.

The team believes the second stage was a result of the comet dust spreading which reflects more sunlight.

Once it reached peak brightness, Wirtanen began to fade over a period of two weeks – the entire outburst lasted for a total of 20 days.

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.’

The burst lasted for 20 days and ejected 2.2 million pounds of material- and NASA used a series of images to create a timelapse of the event

The burst lasted for 20 days and ejected 2.2 million pounds of material- and NASA used a series of images to create a timelapse of the event

There was an hour-long flash followed by a more steady second stage that gradually become brighter over the next eight hours after the outburst. The team believes the second stage was a result of the comet dust spreading which reflects more sunlight

There was an hour-long flash followed by a more steady second stage that gradually become brighter over the next eight hours after the outburst. The team believes the second stage was a result of the comet dust spreading which reflects more sunlight

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Once it reached peak brightness, Wirtanen began to fade over a period of two weeks – the entire outburst lasted for a total of 20 days

Once it reached peak brightness, Wirtanen began to fade over a period of two weeks – the entire outburst lasted for a total of 20 days

‘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 team estimated that a massive 2.2 million pounds of ice and dust was ejected from the burst. 

 ‘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,’ said Farnham.

‘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.

It is not currently known what causes outbursts, but they are related to the conditions on the comet's surface. Pictured is an image of Wirtanen in 2018

It is not currently known what causes outbursts, but they are related to the conditions on the comet’s surface. Pictured is an image of Wirtanen in 2018

Wirtanen was first spotted orbiting the sun in the 1940s, but last year it it came within 30 times the distance to the moon

Wirtanen was first spotted orbiting the sun in the 1940s, but last year it it came within 30 times the distance to the moon

‘We did so and were very surprised!’

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

However, many comets are known to experience occasional spontaneous outbursts that can significantly, but temporarily increase the comet’s activity.

It is not currently known what causes outbursts, but they are related to the conditions on the comet’s surface.

The researchers have suggested a few things that could have occurred, including a thermal event, which is when a heat wave penetrates into a pocket of highly volatile ices, causing the ice to rapidly vaporize and produce an explosion of activity.

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They also propose it could have been a chemical event, where a cliff collapses, exposing fresh ice to direct sunlight.

NASA explained that ‘studies of the outburst behavior, 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 for the first time Wirtanen’s dust trail. 

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 travels 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.

WHAT IS THE TESS SPACECRAFT?

NASA’s new ‘planet hunter,’ set to be Kepler’s successor, is equipped with four cameras that will allow it to view 85 per cent of the entire sky, as it searches exoplanets orbiting stars less than 300 light-years away.

By studying objects much brighter than the Kepler targets, it’s hoped TESS could uncover new clues on the possibility of life elsewhere in the universe.

Its four wide-field cameras will view the sky in 26 segments, each of which it will observe one by one.

In its first year of operation, it will map the 13 sectors that make up the southern sky.

Then, the following year, it will scour the northern sectors.

‘We learned from Kepler that there are more planets than stars in our sky, and now TESS will open our eyes to the variety of planets around some of the closest stars,’ said Paul Hertz, Astrophysics Division director at NASA’s Headquarters. 

‘TESS will cast a wider net than ever before for enigmatic worlds whose properties can be probed by NASA’s upcoming James Webb Space Telescope and other missions.’

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Tess is 5 feet (1.5 meters) wide and is shorter than most adults.

The observatory is 4 feet across (1.2 meters), not counting the solar wings, which are folded for launch, and weighs just 800 pounds (362 kilograms). 

NASA says it’s somewhere between the size of a refrigerator and a stacked washer and dryer. 

Tess will aim for a unique elongated orbit that passes within 45,000 miles of Earth on one end and as far away as the orbit of the moon on the other end.

It will take Tess two weeks to circle Earth.   

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.’

While the current study describes initial results, Farnham, Kelley and their colleagues look forward to further analyses of Wirtanen, as well as other comets in TESS’ field of view.

‘We also don’t know what causes natural outbursts and that’s ultimately what we want to find,’ Farnham said.

‘There are at least four other comets in the same area of the sky where TESS made these observations, with a total of about 50 comets expected in the first two years’ worth of TESS data. There’s a lot that can come of these data.’

 



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