Comet ATLAS breaking up

Comet C/2019 Y4 (ATLAS) is breaking up. The comet was expected to become visible to the naked eye in May.

First signs were reported on 5 April by observers in China who had been monitoring the comet. What had previously been a condensed core to the comet (known as a pseudo-nucleus) appeared elongated, and aligned with the axis of the tail. This behaviour is consistent with a major disruption of the nucleus, according to the observers.

Photographs taken from the UK on the evening of 6 April confirm the changes, as shown in the photos below taken with the same instrument and settings eight days apart.

Observers in Japan, reported on CBET4744, had reported ‘unusual changes’ in the orbit of the comet, due to what appear to be what are termed non-gravitational effects – that is, due to such phenomena as significant gas release. The Bureau issued a new orbit for the comet, but the object now appears to be diverging from the revised positions.

It looks as though the hoped-for comet spectacular in May won’t now be occurring.

See updates below


Changes in comet C/2019 Y4 (ATLAS) over eight days. 200 mm LX90 SCT, Sony A7S camera, 8 sec exposure at ISO 25600. Photo: Robin Scagell

On 3 April, before the breakup became evident, the comet was still displaying a coherent pseudo-nucleus, though with some elongation, as shown in this image by David Davies near Cambridge.

Comet C/2019 Y4 (ATLAS) photographed by David Davies using a 200 mm RC telescope with QSI683 camera. 10 sets of 5-minute RGB subexposures on 3 April 2010 at 21h UT.


On 10 April the comet was still lacking a pseudo-nucleus and had lost brightness. Its orbit is changing slightly from day to day. Photo on on 10 April at 21h UT. 200 mm LX90 SCT, Sony A7S camera, 8 sec at ISO 25600 (4 frames). Photo: Robin Scagell

Update 13 April

The Central Bureau for Astronomical Telegrams reports that ‘CCD images obtained by many observers have shown that the nucleus of this comet has fragmented, causing the comet to lose its sharp central condensation and spread out in clumps of diffuse light that is typical of comets falling apart. ‘ They go on to quote comet expert Zdenek Sekanina as saying that ‘Perihelion survival of C/2019 Y4 is questionable but not ruled out.’

By 13 April 2020 the core of the comet has visibly separated into separate fragments. Meade LX90 SCT, Sony A7S camera. Five 8-second exposures at ISO 25600. Flackwell Heath, Bucks. Photo: Robin Scagell

Update 21 April

Comet ATLAS continues to fragment, although it is still visible as an elongated object at around magnitude 8. The photographs below show it in comparison with the nearby comet C/2017 T2 Panstarrs, with the same instrument and exposure details.

Comet photos
Comets C/2017 T2 Panstarrs and C/2019 Y4 ATLAS, photographed with same instrument and exposure times on 15 April 2020. LX90 and Sony A7S camera, 5 x 8 sec at ISO 25600. Photo: Robin Scagell