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Photo of the planets.

Photo from Solar Orbiter

Planetary rendezvous of Solar Orbiter

Launched in February 2020, Solar Orbiter – a joint collaboration of ESA and NASA – will observe the Sun from closer than any space mission before.

The trajectory to the Sun for this mission is ‘in resonance’ with Venus, which means that it will use Venus for gravity assist flybys. This technique allows the spacecraft to adjust the velocity and alter or tilt its orbit and reduce the amount of time needed to reach close to the Sun.

Aditi Bhatnagar is a Doctoral Research Fellow at RoCS. Photo: UiO

Close to a month before the first gravity assist flyby with Venus (which was scheduled on 27th December), when the Solar Orbiter was about 48 million kilometers from Venus, it observed three of the four rocky planets, i.e, Venus, Earth and Mars, from the Heliospheric Imager (SoloHI) camera on board. The European Space Agency released a video on 26th January 2021, in which the planets are visible in the foreground. The video was also posted on many social media platforms, such as the Facebook page of @RAL_Space_STFC, one of @esa's partners in the mission and Twitter.

Surprised by Uranus

Interestingly, later on, another planet – Uranus – was also found in the image. This happened after a close inspection of the video, when someone spotted another object in the lower left corner which was moving with the background stars, and speculated that it could be Uranus, after checking the planetary positions for 18th November 2020.

This led to further inspection by Mark McCaughrean, Senior Advisor for Science and Exploration at ESA, who confirmed from Celestia planetarium programme and astrometry.net that Uranus is present in the frame, just not where it had been pointed out. What had been spotted was actually a detector artefact, since it doesn't move at all relative to the frame boundaries.

Responsible for the computer programs

Solar Orbiter has ten instruments onboard, six of which are remote sensing telescopes while four are in-situ instruments. The Rosseland Centre for Solar Physics (RoCS) at the University of Oslo is responsible for the computer programs that convert the raw binary data from the remote-sensing instrument SPICE to a format that can be analysed by scientists.

The in-situ instruments will measure the particles surrounding the instrument and will give us a better understanding of the solar wind (a continuous flow of charged particles from the sun which permeates the solar system). This Solar wind reaches out till the Earth and affects the surrounding magnetic environment. It can even cause disruption of satellites in space and  be dangerous for both astronauts in space and ground based technology. Measurements from these instruments will give a better understanding of any harmful changes in the space weather.

Observations from the Solar Orbiter will also help in answering questions such as the heating of the solar atmosphere called coronal heating, and understanding of what drives the magnetic cycle of the Sun.