Apophis’ approach to Earth may mark a new era in planetary defense
We are only five years away from an astronomical event that may remain engraved in the collective memory of humanity. It is about the asteroid Apophis’ close pass to Earth and, although we already know that it will not be dangerous, we can say that it is chilling if we think about it.
For decades, the eyes of the astronomical community were focused on the Earth’s encounter with the cataloged asteroid 99942 Apophis, a rocky body about 340 m in diameter. Although the danger of direct impact has been ruled out, the meeting still attracts great interest. The reason is that this asteroid will approach on April 13, 2029, only about 32,000 km from the surface of our planet.
Although it is not currently on the list of potentially dangerous asteroids in NASA’s Sentry program, Apophis’s approach will be less than a tenth of the distance that separates us from the Moon. And, for the most superstitious, it will happen on Friday the 13th.
At its closest approach to Earth, the asteroid will be perfectly visible to the naked eye. The brightness of the wandering star will reach a stellar magnitude +3, which some of the stars in the Cassiopeia constellation or those in the famous Orion belt have. And, despite its “stellar” appearance, it will be impressive to see it moving at a speed of around the diameter of the Moon per minute.
NASA’s already famous Osiris-REx mission remains operational after visiting and collecting samples from the asteroid Bennu. Due to its capabilities, it has been reconfigured to get closer to Apophis, and renamed Osiris-APEX.
That space mission aims to quantify Earth’s tidal forces on a potentially dangerous asteroid and will take live, never-before-seen images of the asteroid’s surface with our planet in the background. NASA will provide the photograph at the same time we can go out into the garden to see the asteroid above our heads.
Telescopes or binoculars will not be needed. More than 2 billion people in Western Europe and North Africa are likely to attend the upcoming encounter with Apophis, a once-in-a-lifetime experience.
At the time of writing these lines, the European Space Agency (ESA) is also considering launching the RAMSES mission to visit Apophis before, during, and after the asteroid’s encounter with Earth. The mission, proposed in ESA’s Space Security program, would use the same platform planned for the Hera spacecraft and would embark several CubeSat-type satellites to carry out proximity measurements.
To meet Apophis before April 2029, the RAMSES probe should be launched soon. The two possible configurations are to launch it in April 2027 and carry out a flyby of the Earth in April 2028 to position itself on its rendezvous course or to carry out a direct transfer, more expensive and complex, lasting 11 months, in April 2028.
If the ESA Council gives the green light to the mission, the most effective technical solution will be decided in 2025 to reduce costs and allow rapid implementation. A priori RAMSES could encounter Apophis two months before its closest approach to Earth and would carry out a characterization campaign of the asteroid both before and after the encounter.
There is great curiosity in studying whether Apophis is also a pile of debris like Bennu and whether the physiognomy and structure of the asteroid could be affected by gravitational tidal forces.
With the experience of the DART and Hera missions, the use of small satellites or CubeSats to collect proximity data is gaining strength. RAMSES has been proposed to embark at least two CubeSats of six cubic units each, which would be launched towards the vicinity of Apophis before the close encounter. In the chosen environments they would operate independently, using RAMSES as a relay satellite.
Instrumentation will include a thermal infrared camera, laser altimeter, low-frequency radar, dust detectors, seismometers, indenters, microscopes, radiometers, laser retroreflectors, etc. This is a mission that has not yet been decided, but making it a reality in time for the meeting would demonstrate that there are ways to quickly launch this type of mission. After all, perhaps the next asteroid won’t warn us.
It is not a whim to know better the nature and structure of Apophis. Although we can say that it does not pose a risk in the next approaches, at least for a century, in the future it could become complicated.
Our planet’s close encounter with the asteroid Apophis is a once-in-a-millennium opportunity. A high-profile meeting that can be very useful for science, planetary defense, and dissemination. Also, the OSIRIS-APEX mission would give hope in the international cooperation that we need to respond to the challenges that threaten humanity.
– Josep M. Trigo Rodríguez is a Principal Investigator of the Meteorites, Minor Bodies, and Planetary Sciences Group at the Institute of Space Sciences (ICE – CSIC).
*This note originally belongs to The Conversation.