Science

Look up! Newfound Comet Leonard will blaze into view later this year

A recently discovered comet named Leonard could be the brightest of 2021 when it gets closer to the sun at the end of the year – and may even be visible with the naked eye.

The object, catalogued as C/2021 AI, was discovered by astronomer Gregory J Leonard on January 3 at the Mount Lemmon Infrared Observatory in Arizona.

When it was first spotted, the comet was ‘exceedingly faint’, a 16 magnitude object, about 160,000 times dimmer than the faintest stars that can be seen with the naked eye. 

However, by the time it gets to Earth’s orbit later this year, it will be magnitude four or five.

It is getting brighter all the time as it gets closer to the sun, and is currently between the orbits of Mars and Jupiter – expected to be closest to Earth on December 12 when it will be about 35 million km away.

Astronomers are cautiously optimistic Leonard could become a naked eye comet, but say it will only be visible low on the horizon near sunrise from December.

No specific details about the size, shape and structure of Leonard are available as it is so recently discovered, but that is likely to change as it gets closer to the Earth. 

It is getting brighter all the time as it gets closer to the sun, and is currently between the orbits of Mars and Jupiter – expected to be closest to Earth on December 12 when it will be about 35 million km away

Comet C/2021 A1 Leonard on February 12 taken by Pepe Chambo. Since this image was taken it has moved closer to the Earth and will get brighter the closer it gets to the planet

Comet C/2021 A1 Leonard on February 12 taken by Pepe Chambo. Since this image was taken it has moved closer to the Earth and will get brighter the closer it gets to the planet

LEONARD: AN INBOUND LONG PERIOD COMET 

Catalogued as C/2021 AI, comet Leonard is named after the astronomer that first discovered it.

Gregory J Leonard spotted the comet using the Mount Lemmon Observatory on January 3, 2021 .

This was a year before it hit perihelion (the closest approach to the sun).

It last appeared in the inner solar system 70,000 years ago and so is on a 70,000 year orbit of the sun.

This will be its last orbit as it is on a hyperbolic trajectory, meaning it will leave the solar system after its close approach to our host star. 

Comet Leonard is already showing signs of a tail as it begins to warm up on its approach towards the inner solar system, astronomers explained.

It is currently between the orbits of Jupiter and Mars but is heading inwards and will reach its closest approach to the sun around January 3, 2022.

The best time to see it from Earth will be in December this year, with its closest approach to our planet on December 12, 2021 at a distance of about 35 million km.

Its visual magnitude may be about four, which is enough for it to be visible with the naked eye – although it will be very close to the horizon, similar to NEOWISE in 2020.

‘We still might get very good views using binoculars during the days before closest approach to Earth, in early December 2021, with visibility to the eye alone still a possibility,’ explained EarthSky.

When Leonard does make its closest approach it will be best viewed through binoculars, small telescopes and a long exposure camera. 

The comet has a hyperbolic orbit – that means once it passes the sun it will be ejected out of the solar system and never seen again from Earth.   

It hasn’t always been on a trajectory out of the solar system – until this trip around the sun the comet had a roughly 70,000 year orbital period.

Leonard likely spent about 35,000 years coming inbound from about 520 billion km away and may have last visited the inner solar system about 70,000 years ago.

Being an older comet that has felt the effects of the sun before is good news for sky watchers hoping to see the ball of ice in all its glory, complete with tail.

A comet that has never passed the sun before – one created in the Oort cloud at the edge of the solar system – is covered in volatile material including carbon dioxide, nitrogen and carbon monoxide that vaporise as they approach the sun.

This causes a very bright period but it slows then all but disappears as it gets close to the Earth and the sun – making it unlikely to be naked-eye visible.

Comet Leonard is already showing signs of a tail as it begins to warm up on its approach towards the inner solar system, astronomers explained

Comet Leonard is already showing signs of a tail as it begins to warm up on its approach towards the inner solar system, astronomers explained

However, a comet like Leonard that has seen the sun before, has lost some of the volatility and is more likely to be able to hold on to its brightness as it gets closer.

Leonard is also a rapidly moving comet – travelling at 254,399 km per hour relative to the Earth – that is 70.6 km per second. 

Writing for Space.com, guest lecturer at the Hayden Planetarium , Joe Rao, said Leonard was unlikely to become another NEOWISE.

Leonard likely spent about 35,000 years coming inbound from about 520 billion km away and may have last visited the inner solar system about 70,000 years ago

Leonard likely spent about 35,000 years coming inbound from about 520 billion km away and may have last visited the inner solar system about 70,000 years ago

Last year NEOWISE, a long period comet, was visible in the night sky around most of the world including a long, clear tail – making it one of the brightest naked eye comets in years.

‘Comet Leonard will be hidden by the brilliant solar glare during this time, rapidly receding from both the sun and Earth after Jan. 3 of next year and quickly fading away,’ said Rao. 

‘The best, I think, we can hope for is a modestly bright naked-eye comet that will be available to anyone who cares to get up before sunrise during early and mid-December mornings.’   

Explained: The difference between an asteroid, meteorite and other space rocks

An asteroid is a large chunk of rock left over from collisions or the early solar system. Most are located between Mars and Jupiter in the Main Belt.

A comet is a rock covered in ice, methane and other compounds. Their orbits take them much further out of the solar system.

A meteor is what astronomers call a flash of light in the atmosphere when debris burns up.

This debris itself is known as a meteoroid. Most are so small they are vapourised in the atmosphere.

If any of this meteoroid makes it to Earth, it is called a meteorite.

Meteors, meteoroids and meteorites normally originate from asteroids and comets.

For example, if Earth passes through the tail of a comet, much of the debris burns up in the atmosphere, forming a meteor shower.




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