Humanity's Asteroid-Earth Rescue Plan

Under the coastline of Mexico's Yucatan Peninsula lies the second largest meteorite crater on Earth, the Chicxulub Crater. In the early 21st century, researchers calculated and simulated that this huge crater originated from an asteroid named Baptistina. This may sound like a difficult and unfamiliar name, but let's put it another way: For a long time, this asteroid was widely believed to be one of the "culprits" that ended the dinosaur era.

Simulating the formation of the Chicxulub crater

https://www.nytimes.com/

Before the discovery of the crater in the Yucatan Peninsula, a team led by Nobel Prize winner in Physics Luis Alvarez proposed the famous " Alvarez hypothesis " - the arrival of an asteroid caused the extinction of many Cretaceous ancient creatures including dinosaurs. Although there are many different opinions in the relevant field about the relationship between the Chicxulub crater and this extinction event, everyone has a consensus: an impact event that can leave such a large crater in the strata can change the fate of almost all creatures on this blue planet at any time.

In the 18th century, people's research on the solar system was not as profound as it is today. As the planets were discovered by astronomers, the "Titius-Bode Law" - an empirical law describing the average distance between the planets in the solar system and the sun - gradually spread. This law, which has now been proven to have almost no physical meaning, laid the foundation for the discovery of the first asteroid, Ceres. As more and more asteroids are discovered by astronomers, as part of the cosmic ocean that humans have looked up to and tried to explore since ancient times, they have also become frequent visitors to science fiction works.

Asteroid belt diagram

Arthur Clarke, a famous British science fiction writer (if you are unfamiliar with this name, he is more widely known as one of the screenwriters of "2001: A Space Odyssey"), once published a short science fiction story titled " Hammer of God " in Time magazine in the 1990s.

In 2109, human technology and society have reached unprecedented heights. Bases have been established on the moon and Mars where humans can live freely, and human life expectancy has doubled due to scientific progress. Even this is an era when artificial intelligence with a sense of humor and thinking ability is legally recognized as a "human". Although technology is so advanced, people live in fear all the time - because not far from the earth, there is an asteroid named "Kelly". It is about to collide with the earth, and only humans on the moon and Mars bases can survive.

Hammer of God first edition cover

https://en.wikipedia.org

With the hope of saving all mankind, the spacecraft "Goliah" went to Kelly and installed the thruster named "Atlas" on the asteroid that was about to bring disaster to the earth, so as to push it away from its current orbit in the last few months before Kelly arrived at the earth. However, this hope dissipated with the accidental explosion of the thruster. At the last critical moment, Goliath's captain Singh decided to use the spacecraft's own propulsion power with all the crew members to complete the task that Atlas failed to complete.

Although Kelly eventually passed by the Earth and caused a lot of damage, it was fortunate that it gradually moved away after passing through the atmosphere and did not become a bomb that destroyed humanity. Only the Goliath spacecraft and all its crew members were squeezed together due to the excessive gravity acceleration and remained on Kelly forever.

Imaginary image of spacecraft and asteroid

If you have watched "Alone on the Moon" in the past two months, you may find this plot familiar. In the ending of the movie, facing the "π+" Dugu Yue, like all the crew members of the Goliath, chose to sacrifice in exchange for the continuation of human history. Or, let's turn our attention to the real world - just this Monday, when the DART satellite crashed into the "Dimorphos", did it also have the same tragic sense of mission?

Perhaps we can call ourselves "the miracle of life", but in front of the universe, humans are just an insignificant species like dinosaurs. If the asteroid that visited the Earth 65 million years ago had the ability to bring disaster, then we cannot rule out that humans will eventually face threats one day.

As the B612 Foundation (a non-profit organization dedicated to protecting the Earth from asteroid impacts) said, "The Earth will be hit by an asteroid 100% of the time", it is just a matter of time. It is worth mentioning that the name of the B612 Foundation comes from the asteroid home of the same name in the famous fable "The Little Prince" - the idea of ​​whether it is possible to "mine" from asteroids or establish human bases on asteroids is often discussed, but for most people, compared with the benefits that asteroids may bring, the collision risks they carry may be more critical.

Photos of DART after its collision with Dimorphos

https://www.newscientist.com/

This is exactly the meaning of the Double Asteroid Redirection Test (DART): starting now, working for the future of the human species. Faced with the potential threat of an asteroid colliding with the Earth, people already have some alternative response strategies. A more extreme method is to install an explosive device on the surface or under the surface of a celestial body to affect its orbit by changing the mass and structure of the asteroid itself; another way is to launch a heavy spacecraft near the asteroid, and use a period of gravity to slowly push it away from the orbit that threatens the Earth. The strategy of the DART mission is a more compromise approach - to let the spacecraft collide directly with the asteroid at a calculated time, and achieve the purpose of making it deviate from its orbit by changing its momentum.

The DART mission led by NASA is the world's first test of asteroid defense technology. The "double asteroid" about 11 million kilometers from the Earth - a system consisting of a "twin" asteroid Dimorphos with a diameter of about 160 meters and another "twin" asteroid Didymos with a diameter of about 780 meters - is the target of the DART mission. Although the two asteroids themselves do not pose a threat to the Earth, on the one hand, scientists have mature ways to observe their orbital changes, and on the other hand, because they are not particularly close to the Earth, there will be no accidental rush to the Earth after the impact, so this double asteroid system has become the most suitable test target.

"Signal loss" - a situation that people often don't want to hear in space missions, but at this moment it means a milestone success. The satellite, weighing about 600 kilograms, was launched in November 2021 and performed several optical calibrations and orbit corrections on the way to the target location. The DRACO camera on the DART satellite monitored the binary asteroid system in July of this year, two months before the impact mission. After months of preparation, the DART satellite finally crashed into the smaller of the binary asteroid system, the "twin asteroid" Dimorphos, at 7:14 am Beijing time on September 26, at a speed of 6 kilometers per second. The DRACO camera recorded the last moments before the impact.

The last image taken with the DRACO camera

https://www.sciencealert.com/

According to expectations, after the impact, the orbital period of the binary asteroid system will be shortened to a certain extent, and the distance between Dimorphos and Didymos will also decrease. Although the change may be less than one percent, it is precisely such a seemingly insignificant change that breeds the confidence of mankind to resist possible asteroid impact events.

Of course, this collision is not just the end of the DART satellite's mission, but also the beginning of a series of new explorations. Accompanying DART on the journey is the small satellite LICIACube, which separated from DART 15 days before the impact to take images after the impact. Astronomers will continue to use ground-based telescopes to observe Dimorphos and Didymos and record the impact of DART on the asteroids. Two years later, the European Space Agency will launch the Hera mission and arrive near the binary asteroid system in 2026 for an investigation expected to last about half a year to determine the final impact of the collision between DART and Dimorphos.

Three images taken by the Hubble Space Telescope after the DART satellite impact with Dimorphos

https://www.nasa.gov/

Time-lapse image taken by the Webb Space Telescope after the DART satellite impact with Dimorphos

https://www.nasa.gov/

In the past few days, dozens of large telescopes around the world have focused their lenses on the impacted binary asteroid, including the Hubble Space Telescope (HST) and the Webb Space Telescope (JWST) in orbit. From the images sent back by the Hubble Space Telescope, it can be seen that the brightness of the binary asteroid system has increased significantly and steadily after the impact; the near-infrared camera (NIRCam) on the Webb Space Telescope also recorded the continuous ejection of plumes near the impact site.

As of September 27, 2022, astronomers have reported the discovery of 29,933 near-Earth asteroids, one-third of which are larger than 140 meters in diameter, and nearly 1,000 of which are 1 kilometer in diameter. Although the possibility that most asteroids will bring danger to the Earth is negligible, even with a tiny probability, we do not want it to be the reason for the end of humanity.

Known Near-Earth Asteroids (NEAs)

https://cneos.jpl.nasa.gov/

Whether it is the detection of asteroids, the search for potentially dangerous celestial bodies, or personal tests like the DART satellite, all efforts are for the sake of if one day we really discover that small celestial body that is getting closer and closer and destined to head for the Earth, what humans can do besides praying is to use technology to protect ourselves and safeguard the future.

References:

[1]https://www.inquisitr.com/4881237/earth-will-be-hit-by-an-asteroid-with-100-percent-certainty-says-space-watching-group-b612/

[2]https://www.sciencealert.com/behold-the-epic-last-images-taken-by-nasas-asteroid-redirection-test-spacecraft

[3]https://en.wikipedia.org/wiki/Asteroid_impact_avoidance#Further_reading

[4]https://www.planetary.org/space-missions/dart

[5]https://cneos.jpl.nasa.gov/stats/totals.html

Author: Tong Yilu is a master's student at the National Astronomical Observatory. Her research direction is galaxy formation and evolution.

Source: China National Astronomical Service

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