NEOMIR: a European telescope to detect dangerous asteroids

NEOMIR: a European telescope to detect dangerous asteroids
NEOMIR: a European telescope to detect dangerous asteroids

Some near-Earth asteroids are a danger, an unlikely danger, but one that we can theoretically prevent or mitigate entirely by detecting the vast majority of bodies that could collide with our planet. The problem lies with asteroids of approximately 300 to 500 meters. Below that figure there are many more asteroids, but being smaller the potential damage would also be smaller. And above that figure there are fewer asteroids and the percentage of discovered objects is significantly higher. But, specifically, within the population of hazardous asteroids (PHAs), the worrying ones are those objects that approach the Earth in the direction of the Sun, which can go unnoticed as if it were a World War II fighter plane approaching the enemy with the Sun at its back. A key tool for discovering new asteroids is infrared space telescopes, but at the moment we have not launched any specifically designed for this task.

NEOMIR observing asteroids from ESL1 (ESA/Pierre Carril).

NASA plans to launch NEOCam, an infrared space telescope to discover near-Earth asteroids (NEOs), in 2027, but the more eyes there are watching, the easier it will be to spot a body that approaches Earth by surprise. The European Space Agency (ESA) has its own proposed mission of this type, NEOMIR (Near-Earth Object Mission in the Infra-Red). NEOMIR is intended to complement NEO Surveyor. But while NASA’s telescope must fulfill the goal, mandated by the US Congress, of discovering 90% of asteroids larger than 140 meters in diameter, NEOMIR will focus on smaller objects. Located around the Earth-Sun system’s L1 Lagrange point, 1.5 million kilometres away, NEOMIR will be able to detect objects larger than 20 metres in diameter that are about to pass close to Earth at least three weeks in advance, allowing possible impact zones to be evacuated should they collide with our planet.

NASA’s NEO Surveyor will detect larger, more distant asteroids, while NEOMIR will focus on smaller, closer objects (NASA).
Infographic on the danger of asteroids (ESA).

NEOMIR will be dedicated to observing the sky in search of asteroids, being able to point up to 30º from the Sun at most (NEO Surveyor will only be able to get as close as 45º). It will incorporate a telescope with a 50-centimetre diameter main mirror and two infrared sensors to cover the infrared spectrum from 5 to 10 microns. The choice of these wavelengths ensures that more bodies can be discovered, since the peak emission of a nearby asteroid with a temperature of about 300 kelvin is at 9 microns (most NEOs have temperatures between 200 and 400 kelvin). The great challenge of the mission is to cover the same area within a few hours of each other in order to detect an asteroid that is coming directly towards us and, therefore, leaves hardly any trace in the images, which requires covering a large field of view in a short time (with exposure times of approximately one minute).

NEOMIR (ESA) field of view and sky scanning strategy.
Simulated population of near-field asteroids (black dots) as a function of time to impact. NEOMIR (orange) will be able to detect asteroids that ground-based telescopes (blue) or NEO Surveyor (red) will not be able to (ESA).

NEOMIR will be able to detect asteroids larger than 20 to 25 metres in diameter from 15 million kilometres away at least 3 to 4 weeks in advance, but obviously an asteroid will always slip through. However, the mission has been designed to detect at least any object larger than 20 metres that approaches Earth within 1.5 million kilometres, or about two days from its encounter with our planet. NEOMIR will have a field of view of 1.7º x 7º and will scan the sky around the Sun in three concentric rings from 30º to 51º from the Sun. Each field of 1.7º x 7º will be observed four times in 39 hours. If NEOMIR is finally approved, and we hope it is, it would take off no earlier than 2030 on an Ariane 62.


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