Comet travelling towards Earth 'could be from outside our solar system'

The new comet is known as Comet C/2019 Q4
Frantisek_Krejci/Pixabay
Matt Drake13 September 2019

An amateur astronomer has discovered a mysterious comet that could be from outside our solar system.

Amateur stargazer Gennady Borisov made the discovery on August 30 at the Crimean Astrophysical Observatory in Bakhchysarai.

At the time, the comet was about 450 million km from the Sun.

The Harvard University Minor Planet Centre (MPC) has issued a formal announcement of the discovery.

It could be the second interstellar object discovered after the elongated body known as 'Oumuamua was identified in 2017.

'Oumuamua travelling towards the outskirts of our solar system
NASA/ESA/STScI

According to the BBC, the new comet - known as Comet C/2019 Q4 (Borisov) - appears to have a "hyperbolic" orbit, which deviates substantially from that of a perfect circle, indicating its origin is from another planet.

A perfect circle has an eccentricity of 0 and elliptical orbits of many planets and comets have eccentricities between 0 and 1. The new object has an eccentricity of 3.2, based on current observations.

'Oumuamua was initially classified as a comet based on its hyperbolic trajectory.

But further observations detected no sign of a coma, which is the fuzzy envelope around the nucleus of a comet.

C/2019 Q4 (Borisov) is clearly an active comet with a visible coma and tail.

Astrophysicist Karl Battams, from the Naval Research Laboratory in Washington DC, tweeted: "Unlike 'Oumuamua, whose asteroid-or-comet nature still gets debated, this one is definitely a comet.

"If it is unequivocally interstellar, it'll be fascinating to see how its composition (spectral properties) compares to the variety we see in comets from our own Solar System."

Astrophysicist Simon Porter, from the Southwest Research Institute (SwRI) in San Antonio, Texas, said: "With such a bright coma, we should be able to get beautiful spectra of Q4 and hopefully measure isotopic ratios."

The object is also very large, around 20km wide, and bright - unlike 'Oumuamua.

What's more is that 'Oumuamua was only spotted after its closest approach (perihelion) to the Sun so wasn't visible long enough for astronomers to answer the questions they had.

But C/2019 Q4 (Borisov) is still approaching our Solar System and won't reach perihelion until December 10.

The Minor Planet Centre said the object should be observable for at least a year and has called on astronomers to make follow-up observations.

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