Now entering the detailed study phase, Comet Interceptor aims to​ investigate a dynamically-new comet or interstellar object approaching the Sun for the first time to improve our understanding of the origins of our solar system and the wider universe.

Comets are some of the most primitive objects in the solar system, time capsules from the period when Earth and the other planets formed; however, a pristine one has yet to be encountered and explored.

Such objects are difficult to target because they can only be discovered when approaching the Sun for the first time, leaving little time to plan and launch a mission to them.

All comets encountered by space missions to date, such as by ESA’s highly successful Rosetta, have been altered by multiple approaches to the Sun due to their short orbits. These encounters change their surface, hiding their original appearance and make-up under thick layers of dust.

Until recently, pristine comets have been discovered typically months to a year before they reach the inner solar system, allowing far too little time to launch a spacecraft to investigate them.

To address these challenges, Professor Geraint Jones (UCL Space & Climate Physics, and The Centre for Planetary Sciences at UCL/Birkbeck) and Dr Colin Snodgrass (University of Edinburgh) led an international team from Europe, Japan, and the USA that proposed Comet Interceptor – a multi-spacecraft ‘fast’, or F-class mission.

The ‘fast’ refers to the implementation time, with a total development duration from selection to launch readiness of about eight years. F-class missions, which have a launch mass of less than 1000 kg, will share the ride into space with a medium-class mission, taking advantage of additional space in the launcher and the boost to the Sun-Earth Lagrange point L2, which is 1.5 million kilometres ‘behind’ Earth as viewed from the Sun.

After Comet Interceptor arrives at L2, one main spacecraft (A), which will act as the communications hub, and two sub-spacecraft (B1 and B2), for multi-point observations around the target, will lie in wait as one.

Once a suitable target is found using Earth-based telescopes, the spacecraft stack will be directed to it. Just before reaching the comet, the three craft will separate, and will together characterise the comet’s surface composition, shape, structure and the gases it is releasing.

“We’re thrilled that ESA has selected Comet Interceptor as its first F-class mission. It’s an extremely ambitious and exciting project to encounter and explore a true, pristine comet or interstellar object for the first time by catching it on its first approach to the Sun,” explained lead proposer Professor Geraint Jones.

“We simply wouldn’t have been able to do it until now as the mission relies on recent and ongoing breakthroughs in the technical capability of ground-based survey observatories to find targets. With Comet Interceptor, we’ll be able to respond quickly to study one of the most important and ancient objects from our Solar System and maybe beyond.”

The new Large Synoptic Survey Telescope (LSST), currently under construction in Chile, is expected to make an important contribution – it will scan the whole visible sky every few nights, and will discover comets coming from the outer Solar System at much larger distances than current telescopes.

The team will work with scientists and engineers at ESA and the Japan Aerospace Exploration Agency (JAXA) to develop Comet Interceptor, which will carry equipment developed and built at the UCL Mullard Space Science Laboratory as part of its comprehensive international suite of scientific instruments.

Spacecraft B2 will carry EnVisS (Entire Visible Sky Coma Mapper) – the UCL-led camera which will map the entire sky within the comet’s head and near-tail, to reveal changing structures within the dust, neutral gas, and ionized gases.

Other instruments will return high resolution images of the comet’s nucleus, measure its composition directly and indirectly, and study how the comet interacts with the interplanetary magnetic field and the flow of charged particles from the Sun.

Dr Colin Snodgrass, added: “It is great that ESA has recognised that this is the perfect opportunity for this mission. It takes maximum advantage of the launch to L2, lets us respond to the exciting discoveries we expect from the LSST, and most importantly continues the great work on comets that has come from the Rosetta mission. It makes a lot of sense to do this while we have an active community of space scientists in Europe, and an experienced engineering team at ESA, who know the unique challenges of a mission to a comet.”

Comet Interceptor will be launched as a co-passenger with the ARIEL (Atmospheric Remote-sensing Exoplanet Large-survey) mission led by Professor Giovanna Tinetti (UCL Physics & Astronomy, and The Centre for Planetary Sciences at UCL/Birkbeck).

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  • Comet Interceptor concept (credit: ESA)

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