On March 31, 2017, Jupiter’s moon Europa passed in front of a rear star – a rare event captured for the first time by ground-based telescopes thanks to data provided by the ESA Gaia spacecraft.
Previously, spectators had only watched two of Jupiter ‘s other branches – Io and Ganymede – at an event like this.
Gaia has been working in space since late 2013. The mission aims to make a three-dimensional map of our galaxy, and identify the big stars that call the Milky Way home. It has been hugely successful to date, featuring over a billion star locations and trends.
Knowing the exact locations of the stars we see in the sky will allow scientists to predict when different bodies in the solar system pass in front of a star from a particular vantage point. : an event called stellar occultation.
Gaia is no stranger to such events – the spacecraft helped astronauts take a unique look at Neptune’s lunar Triton as it went in front of a distant star in 2017, revealing more about atmosphere and the properties of the moon.
Ocultations are extremely valuable; they enable a measure of the features of the frontal body (size, shape, position, and more), and can reflect structures such as rings, jets, and atmosphere. Such measurements can be made from the ground – something Bruno Morgado from the Brazilian National Observatory and LIneA, Brazil, and his colleagues took to study the moon Jupiter, Europa.
Jovian odyssey at JUICE. Click here for details and large versions of the video. Credit: ESA
“We used data from Gaia’s first data release to predict that Europa, from our perspective in South America, would pass in front of a bright star in March 2017 – and to predict the place best to see this occultation, ”said Bruno, lead researcher of a new paper reporting results from occultation 2017. Gaia’s first data release was released in September 2016.
“This has given us an amazing opportunity to study Europa, as this method offers the same accuracy as images obtained by space explorers. ”
Gaia data showed that the event would be seen from a thick band sliding from the northwest to southeast across South America. Three observatories in Brazil and Chile were able to capture data – a total of eight sites tried, but many had bad weather.
Adhering to previous measurements, the observations updated the radius of Europa to 1561.2 km, determined the position of Europa in space and with respect to its host planet, Jupiter, and marked the shape of the moon. Rather than just as spherical, Europa is known as an ellipsoid. The observations show the moon to measure 1562 km when measured transversely in one direction (the so-called ‘semi-major’ axis), and 1560.4 km when measured over the other direction. (the similar ‘semi-minor’ axis).
Upcoming stellar events with Jupiter’s four biggest moons. Credit: ESA / Gaia / DPAC; Bruno Morgado (Brazilian National Theater / LIneA, Brazil) et al. (2019)
“It is very likely that we will be able to see many more events like this with the Jupiter branches in 2019 and 2020,” said Bruno. “Jupiter passes through a range of sky with the galaxy center in the background, making it much more likely that its branches will pass in front of bright stars. This would help us to find their three-dimensional shapes and positions – not only for Jupiter’s four largest branches, but also for smaller, irregularly shaped ones. ”
Using Gaia’s second data release, released in April 2018, the scientists predict the dates of more occultations of bright stars with Europa, Io, Ganymede and Callisto in the coming years. , and lists 10 events in total through 2019 and 2021. Future events will include stellar occultations with Europa (22 June 2020), Callisto (20 June 2020, 4 May 2021), Io (9 and 21 September 2019, 2 April 2021), and Ganymede (25 April 2021).
Three have already occurred in 2019, two of which – stellar occultations by Europa (June 4) and Callisto (June 5) – were observed by the researchers, and the data are still under investigation.
Upcoming events will be seen even with amateur telescopes as small as 20 cm from different regions around the world. Jupiter’s favorable position, with the galactic plane at the back, will not happen again in 2031.
The largest branches of Jupiter. Credit: NASA / JPL / DLR
“Stellar occultation studies allow us to learn about branches in the solar system from afar, and are also relevant for future missions visiting these worlds,” says Timo Prusti, ESA Gaia Project Scientist . “As this result shows, Gaia is a very flexible mission: it not only enhances our knowledge of stars, but also of the wider solar system. ”
Proper knowledge of Europa orbit will help prepare space missions aimed at the Jovian system such as ESA’s JUpiter ICy moons Explorer (JUICE) and NASA’s Europa Clipper, both of which are set to launch in the next decade.
Upcoming stellar events with Jupiter’s four biggest moons. Credit: ESA / Gaia / DPAC; Bruno Morgado (Brazilian National Theater / LIneA, Brazil) et al. (2019)
“These kinds of ideas are very interesting,” says Olivier Witasse, JSA’s JUICE Project Scientist. “JUICE will reach Jupiter in 2029; Our best knowledge of the lunar position of the system will help us prepare for future mission navigation and data analysis, and design all the science we intend to do.
“This science is up to us to know things like round moon signals and to understand how close a spaceship comes to a particular group, so the better our knowledge, the better. who will do this planning – and the subsequent data analysis. ”
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