Jupiter’s moon Europa to obscure distant star
On 19 June 2022, Jupiter’s intriguing moon Europa will pass in front of a distant star, making that star appear to disappear for at least a minute. This event will be easy to see with any size of telescope from certain parts of Africa.
By timing the event and then comparing the observations from different viewing locations astronomers will be able to refine their understanding of Europa’s orbit in preparation for ESA’s JUpiter ICy moons Explorer (Juice) mission, which is scheduled to arrive at the system during 2031. They may also be able to investigate the way the starlight interacts with the tenuous envelope of gasses that surround Europa.
When one celestial object blocks the light of a more distant one, it is called an occultation. The prediction for this particular occultation has been made using data from ESA’s Gaia mission.
Operational since late 2013, Gaia is a star mapping mission that is recording the precise positions of more than a billion stars in our home galaxy, the Milky Way. On 13 June, its much anticipated third full data release (DR3) will be made publicly available.
DR3 will contain almost 2 billion celestial objects. Using data from previous Gaia releases has already allowed improved predictions to be made for several previous occultations, increasing the chances of observational success.
For example, in 2017, Gaia data was used to predict a Europa occultation that was to occur on 31 March. At the time, the only Jovian moons that had been observed in this way were Io and Ganymede. So, thanks to Gaia’s prediction, astronomers on Earth observed a Europa occultation for the first time.
Gaia data were subsequently used to predict further occultations involving all four of Jupiter's largest moons. Known as the Galilean moons because they were discovered by Galileo Galilei, they are Io, Europa, Ganymede and Callisto.
What makes the upcoming occultation of Europa special is that this moon will be in Jupiter’s shadow at the time and so it is impossible to see Europa directly because it does not generate any light of its own. Instead, it is visible only when it reflects sunlight. As Jupiter will be blocking that sunlight during the occultation, observers will only know Europa is there when it makes the star temporarily disappear.
The occultation takes place at 03:05:57 UTC, and it is only visible across a rather narrow track of the Earth’s surface. The centre line of that track passes through the African countries of Namibia, Botswana and Zimbabwe. Eastwards from here, it will be lost from view by the rising Sun.
The occulted star is below the limits of visibility to the naked eye but is not too faint. With an apparent brightness of magnitude 9, it will be easily visible in any size of telescope. To find it on the sky, astronomers should look at coordinates RA: 00:23:46.52, Dec: +01:13:18.92.
Observations of the event can be sent to europaocc2022.imcce@obspm.fr.
Being able to refine the orbital position of Europa, and the other moons of Jupiter, will make ESA’s Juice mission more productive. It will help spacecraft operators navigate between these icy worlds more accurately, and it will help the scientists extract conclusions from the flyby data. For example, knowing the spacecraft’s exact altitude above a moon’s surface will make calculations about the moon’s interior more precise.
This prediction is a reminder of the many facets of astronomy that Gaia data can be used for and how star data can help out with the study of asteroids and moons in our Solar System. Some details for Europa and some of the other moons of Jupiter will be part of the upcoming Gaia data release 3, to be released on 13 June.