Comet 103P Observing Campaign


We are very happy to be working with Giannantonio Milani and the CARA project on the Comet 103P/Hartley Observing Campaign.   

Giannantonio says:  Comet 103P was explored by a spacecraft (Deep Impact/EPOXI Mission) and so is one of the few comets that we know well in detail and it is always important to monitor its evolution in time. In 2010 it displayed a quite unusual behavior with an intense fast variability around perihelion. I don't remember another comet that did this. Surely the unusual shape of the nucleus and its rotation played an important role in this.

Surprisingly the current apparition is showing a less active behavior; a tendency for activity to decrease over time is normal in a comet as with each revolution around the sun it loses volatile material and the amount of inert dust accumulated on the surface increases, for instance on comet 67P it was seen that as much as 90 per cent of the dust ejected fell back onto the surface.

For more background on the comet take a look at NASA 

Update 16/11/2023

The observing campaign on comet 103P/Hartley is progressing successfully and many very good images and data have been collected, many contributions have come from Comet Chasers and the Faulkes Project and LCO.

A brief overview of some images illustrates better than 1000 words the quality of what we are collecting. The elaborations highlight the particular morphology of this comet and will help to better understand what is happening. In the processed images, the circular diffuse halo is mostly due to gas emitted from the nucleus and expanding, while the thin tail is due to dust escaping from the nucleus at a very low speed and pushed away from the light of the Sun.

As the comet moves away from the Sun it is now beginning to weaken. It will still be important to follow its progress throughout its appearance.

Compared to 2010/11, 103P has shown very different behaviour, although it has some common characteristics. Dust production this year appeared roughly halved and the brightness maximum fell later than in 2010.

The light curve shows measurements of the amount Af[rho], a strange measurement that provides us with information on how much sunlight is reflected by the dust, and thus also on the dust itself. The time is expressed in days before and after the perihelion (that is when the comet reached the minimum distance from the Sun), occurred on October 12. The current data are compared with the 2010/11 ones.

There were also unusual rapid changes in brightness in this apparition, but later than in 2010. The Faulkes/LCO observations from schools have been valuable precisely for observing these fluctuations in detail. The nature of these variations is in many ways still mysterious.

We think that the peculiarities of this strange comet may depend on the strange shape of the nucleus and its rotation, which, as the nucleus is very small and elongated, can occur in a complex manner. But not all Is still clear and there may be other phenomena that we hope to understand from all the observations collected.

Not all the images have been measured and the analysis made so far is only preliminary. A thorough analysis and check on all the data will be completed only at the end of the observing campaign.


The 103P decrease in activity now seems excessive, however, and it is possible that the comet will hold some surprises in the coming weeks, after perihelion. For example, the rapid variations of 2010 have not yet been observed. We'll see them later? Or nothing will happen? We therefore have no idea about what may happen.


The preliminary results from the 103P/Hartley campaign shows that this year the comet is displaying a different behavior than in 2010/11, with a much lower general dust production at perihelion.

Afrho refers to a 5000 km window at the comet and it is corrected to a zero phase angle.

Comet 103P

Image taken by St Mary's Catholic Primary School Bridgend.

14 October 2023 10:08 -10:13 - 1m telescope, R,V,B filters, at McDonald Observatory, Texas, USA

Comet 103P

Image taken by Junior High School Heraklion, Greece.

7 November 2023 15:25 - 2m telescope, r' filter, Faulkes Telescope North, Haleakala, Hawaii, USA