NASA, ESA Mull Earth’s First Planetary Defence Mission

Scientists from the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) attended the EPSC-DPS Joint Meeting 2019 in Geneva this week. One of the interesting things on their agenda was discussing the effectiveness and potential implications of asteroid-deflection techniques.

Why is that important? Well, even modest space rocks can cause huge destruction on Earth. Fortunately for humans, an asteroid like that has not come our way for millions of years. However, scientists believe it is crucial to be prepared for such a catastrophic prospect all the same. And that’s what the NASA-ESA joint initiative Asteroid Impact and Deflection Assessment (AIDA) aims to do.

While scientists are already capable of tracking and predicting asteroid trajectories, we may also possess the technology to change an asteroid’s course. AIDA intends to put this very technology to test starting July 2021, by conducting a trial run.

The AIDA has designed a two-phase mission, which will begin with NASA’s Double Asteroid Redirection Test (DART) launch in July 2021, and its subsequent collision with asteroid ‘Didymos B’ in September 2022. In the second phase, ESA’s Hera mission will visit the same asteroid in 2027, to investigate the outcome of the impact.

Why Didymos B?

Didymos B, also known as “Didymoon”, is part of the near-Earth binary asteroid, Didymos. Despite not posing any direct threat to the Earth, this moonlet has been identified as an apt target due to two major reasons.

First, this rock is similar in diameter (i.e. 100-200 metres) to the near-Earth objects that are statistically the most likely to collide with Earth. Second, Didymoon already revolves around another object, and its fixed orbit is well studied. Therefore, even the slightest of shifts in its usual trajectory post impact will be easily picked up by telescopes. And since it orbits in front of as well as behind the primary body, it can also be observed from multiple perspectives.

While DART will serve as an insurance policy for Earth in case of future asteroid emergencies, the Hera mission will be significant in terms of the valuable information it will provide.

Through Hera, the AIDA will try to estimate the efficiency of the kinetic impact by measuring the post-collision mass of Didymos B. It will also conduct a detailed examination of the impact crater, so as to characterise the physical and mineralogical properties of the Didymos asteroid pair.

Studying such properties, along with the overall behaviour of small space bodies during impact, is a critical part of the science of planetary defence, especially considering that existing data on the subject is restricted to models and lab-based experiments. Observation of the huge impact crater created by Japan Aerospace Exploration Agency’s (JAXA) asteroid explorer ‘Hayabusa2’ on asteroid Ryugu in June 2018, and the resultant sand-like behaviour of particles on its surface, has only added to the motivation for this planned collaborative effort.

As of now, the DART mission is being developed by the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, USA. The decision on funding the Hera mission will be taken at the European Ministerial Conference in November this year.