What is planetary defense and why the heck do we need it?

Evidence surrounds you. On a clear-sky night, with a pair of binoculars, you can observe the bombarded surface of the moon. Using slightly fancier tools, the same phenomenon is observable all across the Solar System. Evidence is also present in our planet. Earth’s geological and biological history is punctuated by evidence of repeated and devastating impacts from near-Earth objects (NEOs), asteroids coming close to the Earth.

Historic impacts…

Proof is found not only in the distant past; famous destructive events took place in contemporary history. In 1908, in Tunguska, a 50 meter comet generated a shockwave that levelled 400,000 football fields of trees in Siberia; see Cosmos’s Heaven and Hell for more info. The effects could be felt in distant places such as Paris and London. In February 2013, and once again in Russia, a 20 m object exploded at an altitude of about 30 km injuring 1,491 people in Chelyabinsk.


In the present day…

There are about 1800 potentially hazardous objects (size > 140 m, minimum distance to Earth < 0.05 AU) that have already been catalogued, but this number is increasing.

These events are highly unlikely, but their destructive potential is monstrous. However, the more frequent episodes are destructive enough to pose a considerable hazard on the local level. You can check out Asimov’s A Choice of Catastrophes where he explores this topic. Thus far, we have seen that we are defenseless. We just continue our lives hoping that day never comes.

Monitoring, tracking, discovering

In the US there are currently three ground-based NEO-search programs: the Lincoln Near-Earth Asteroid Research (LINEAR) program, the Catalina Sky Survey (CSS), and Spacewatch. However, strong biases exist against the discovery of objects in some types of orbits, due to the limited portion of observable space from the ground.

NASA, Planetary Defense Coordination Office is in charge of cataloging and tracking potentially hazardous near-Earth objects (NEOs) such as asteroids and comets that are larger than 30 to 50 meters in diameter (compare to the 20-meter Chelyabinsk meteor) and coordinating an effective threat-response and -mitigation effort. The office will continue to utilize the polar orbiting infrared telescope NEOWISE to detect any potentially hazardous object.

At European level, there is the ESA SSA-NEO Coordination Centre. It serves as the central access point to a network of European NEO data sources and information providers now being established under ESA’s Space Situational Awareness (SSA) Programme.

How to prevent asteroid impact

But what if we were able not only to mitigate the effects but also to completely prevent an asteroid from hitting the Earth? Apart from science-fiction examples, based on nuclear bombs, there are many solutions to prevent an asteroid from hitting the Earth. Some are simple, such as the kinetic option, i.e., hitting the asteroid, and the one we have just discussed, the nuclear. Others are a bit more sophisticated such as the thermal/solar (see video) option, painting the asteroid so that light does the job for us, or gravitational, which basically consists of attracting the asteroid to our rocket; see example here.


These two latter options are still science fiction, and would only work if the asteroid is known to be heading for the Earth well beforehand, since their effects are minuscule. For swifter asteroid deflections, the kinetic option is the preferred one and is considered the more mature because it is based on existing and affordable spacecraft technology.

However, is it sufficient to use brute force on an asteroid to deflect it? Have we not learnt anything from Bruce Willis’s mistakes3?

Universe History storytellers

Asteroids, small moons, and comets are not only dangerous objects wandering the Solar System; they might also be the most interesting ones. They are replicas of the primitive Solar System, since they formed in the very early stages and have remained unchanged. This implies that there is an inconceivable amount of invaluable scientific data waiting for us to come and collect it.

Talking more in-depth about NEA missions

Numerous missions have been launched in the past 30 years. Comet exploration started with the Ice space mission in 1978, which observed comet Giacobini-Zinner and Halley.

Since 2002, under the General Studies Programme, ESA has conducted several mission studies such as the Don Quijote asteroid-deflecting experiment as well as In-Orbit demonstration projects such as PROBA missions.

Several NASA space missions have also flown by and observed asteroids. The NEAR Shoemaker spacecraft landed on Eros. Dawn spacecraft traveled to the asteroid belt in 2011 to orbit and study the second largest object there, Vesta and then to Ceres,a “dwarf planet“. In 2016 NASA launched the OSIRIS-REx spacecraft to study a near-Earth asteroid named Bennu.

Between Mars and Earth’s orbit there are two twin boulders orbiting each other; the biggest is called Didymain and the smallest Didymoon. Both constitute the Didymos binary asteroid system and NASA wants to play Armageddon with them (no nuclear bombs involved though).

NASA will send a kinetic impactor, called DART1, to strike Didymoon. Before Ministerial Council 2016, ESA planned to send a spacecraft, called AIM1 (see video), to observe the impact. SPS was involved in the GNC and mission analysis of AIM. However, AIM did not get the necessary support and was finally cancelled. NASA will go ahead with DART but we will not be there to observe the impact.

But remember AIM? It’s back! In HERA form.2

That is where HERA comes in. HERA is meant to perform the first characterization of an asteroid that poses a potential threat to Earth. Additionally, it will measure the momentum transfer to the asteroid of the first asteroid deflection test ever, and potentially the second4. Moreover, the asteroid’s environment is highly perturbed and changing; thus, navigating a spacecraft around it poses a serious challenge that SPS is in charge of. As a summary, HERA is David, fighting against Goliath.

SPS (Spain, Romania, Poland & Portugal) is now involved in such a promising project thanks to its expertise in this field, since it has participated in multiple missions/projects such as  AIM, DAFUS-AIM, NEO-GNC, NEO-GNC 2, Neoshield2, CLEON/CLEON+, CHILON/CHILON-2; Marco POLO, SYSNOVA-BEAST, and Rosetta.

1 We are great at naming space missions, aren’t we?

2 At least, AIM is not back in pog form.

3 This was actually the failure in Deep Impact.

4 A second impact with different conditions is scheduled to be carried out by JAXA.

Author: Victor Moreno

Las opiniones vertidas por el autor son enteramente suyas y no siempre representan la opinión de GMV
The author’s views are entirely his own and may not reflect the views of GMV

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