Two spacecraft, both carrying Imperial kit, are flying by Venus only a day apart, giving a rare opportunity to study the planet’s space environment.

The two European Space Agency (ESA) spacecraft, Solar Orbiter and BepiColombo, are both using Venus as a ‘gravity assist’ to power them towards the inner Solar System, and are passing close to the planet on 9 and 10 August respectively.

It’s a total bonus to be able to do science we’ve never done before, and an exciting possibility to study a different example of how a planet can interact with the solar wind. Professor Tim Horbury

Solar Orbiter is on its way closer to the Sun, while BepiColombo is headed to Mercury, but their double flyby of Venus is providing an unprecedented opportunity to do some extra science, studying the environment around the planet.

Principal Investigator for Solar Orbiter’s magnetometer Professor Tim Horbury, from the Department of Physics at Imperial, said: “If you pitched a double-spacecraft flyby of a planet it would never get funding as it would be so complicated and expensive – and yet we got the opportunity just by chance.

“It’s a total bonus to be able to do science we’ve never done before, and an exciting possibility to study a different example of how a planet can interact with the solar wind.”

Early data

Both spacecraft carry a magnetometer – an instrument that measures magnetic fields in space. The magnetic field from the Sun is carried throughout the Solar System on the stream of charged particles called the solar wind, which can interact with magnetic fields generated by planets.

At Earth, our own magnetic field protects us against the full force of the solar wind, meaning it cannot reach our atmosphere. However, Venus does not generate its own magnetic field, leading to very different interactions between the solar wind and the planet’s atmosphere.

Now, with Solar Orbiter and BepiColombo’s magnetometers both taking data as they fly close to each other around Venus, scientists will get a treasure trove of data revealing the detail of what is going on at the planet, and in the solar wind more generally.

^{The event marks Solar Orbiter's second flyby of Venus as it heads closer towards the Sun. Video credit: ESA/ATG medialab}

The magnetometer aboard Solar Orbiter was completely designed and built at Imperial, where researchers now collect and analyse all the data coming from the instrument. Parts of the magnetometer aboard BepiColombo were also built at Imperial, and researchers have access to its data.

Solar Orbiter has already sent some data from its flyby early this morning (9 August), which Imperial researchers are checking and analysing. Professor Horbury said: "We know that the instrument has worked perfectly and taken good measurements, and we’re really looking forward to looking at the data in detail over the next few days."

Studying the solar wind

Because the two spacecraft will be flying relatively close to each other – within 600,000km, which is about 0.25% of the distance between the Sun and the Earth – the researchers will be able to discern new details both in the solar wind in general and its interactions with Venus’ atmosphere.

For example, researchers have recently discovered the phenomenon of ‘switchbacks’ in the solar wind – long and thin spikes of solar wind that can snap back on themselves.

We have been working on both of these projects for decades, so it’s now so exciting to see science coming out of them, especially together. Helen O'Brien

However, with only one spacecraft flying through one switchback, it’s impossible to know exactly how long and how thin they are. With two, it may be possible to discover the true scale of switchbacks and a host of other finer structures within the solar wind.

The two spacecraft will make complementary measurements of the way Venus interacts with the solar wind, such as the ‘bow shock’ where the solar wind slams into the upper atmosphere, and the tail where it reconnects on the other side of the planet.

Flying close to each other in time, as well as space, also means the researchers will be able to see how elements of the solar wind evolve as they travel out from the Sun and interact with Venus’ atmosphere.

Teaming up for science

Instrument Manager Helen O’Brien, also from the Department of Physics at Imperial, oversaw the construction of both Imperial hardware contributions. She said: “We have been working on both of these projects for decades, so it’s now so exciting to see science coming out of them, especially together.

“Both spacecraft are technically in their ‘cruise’ phases – just getting to their destinations before they start taking science data – but we’ve been so lucky that ESA have allowed both magnetometers to run so we can take advantage of this opportunity to collect data.”

There are plenty more possibilities for Solar Orbiter to do some interesting science on its way to the Sun, including a close flyby of Earth in November for another gravity assist, and opportunities to team up with other spacecraft both near and far from the Earth to examine the solar wind.

Read more about the double flyby on ESA's website and see some of the first photos and data.