In 2006, astronomers from the NASA-backed Catalina Sky Survey in Arizona spotted a peculiar object in the midst of thousands of human-made satellites orbiting Earth. Upon closer examination, they discovered that the object was not just another piece of space debris, but rather a natural satellite that had been pulled into an orbit with Earth, similar to the moon. This natural satellite, also known as a “minimoon,” designated as 2006 RH120, was only a few meters in diameter and traveled around Earth for a year before being ejected from the planet’s orbit. More than a decade later, the Catalina Sky Survey scientists discovered another minimoon, 2020 CD3, about the size of a small car, also orbiting Earth. It was eventually flung out of the Earth-moon system’s influence in March 2020.
Minimoons are of great interest to scientists due to their proximity to Earth. However, some experts have recently considered using these natural satellites, along with other near-Earth asteroids, as potential stepping stones for humanity’s exploration of the universe.
“We have yet to become an interplanetary species,” Richard Binzel, a professor of planetary sciences at the Massachusetts Institute of Technology, told Live Science. Minimoons could become milestones “to achieve as you’re learning how humans can operate in interplanetary space, and ultimately reach Mars.”
Stepping stones – pathway
NASA launched the OSIRIS-REx spacecraft in September 2016, which was an unmanned vessel sent to get a sample from the asteroid Bennu. Bennu is considered as potentially hazardous, with a one-in-2,700 chance of hitting the Earth in 2182. After seven years, OSIRIS-REx returned to Earth with a small fragment of Bennu, which is 4.5 billion years old.
The success of the OSIRIS-REx mission has encouraged scientists to plan the next phases of near-Earth exploration. One of the ideas is to use nearby asteroids as stepping stones for missions to Mars.
Read More News: Earth’s mini-moons: Could they make Us Interplanetary?
According to Binzel, retrieving Bennu was a significant step in the right direction, but there might be a better target to test our technology to explore the cosmos further. Bennu is approximately 186,000 miles (300,000 km) away from Earth, and it only crosses the planet’s orbit around the sun every few years. Therefore, the mission took seven years and cost an estimated $1.16 billion.
On the contrary, Minimoons are some of the most accessible asteroids to reach from Earth, Binzel said.
“To go anywhere in space, you have to change your velocity,” Binzel said. Minimoons are small bodies with very little gravity, and have a low required change in velocity, or delta-V, which means that it doesn’t take much propulsion to transport a spacecraft from low Earth orbit to a rendezvous with the asteroid.
Given these properties, minimoon missions would require less fuel than journeys to many other cosmic bodies. “It only takes a puff of fuel to leave the Mini-Moon and head back towards Earth,” Binzel told Live Science in an email.
According to recent research, it would take around 100 days to travel to a minimoon and return. In comparison, our permanent moon is only three days away, although NASA’s Saturn V rocket required 203,400 gallons (770,000 liters) of kerosene and 318,000 gallons (1.2 million liters) of liquid oxygen just to lift off the ground.
While minimoons present an exciting opportunity for exploration, their short-term nature poses a significant challenge. It could be difficult to plan and execute a mission before the natural satellite is ejected from its orbit around Earth.
“They are in tagalong orbits with the Earth, so they’re like a pet,” Binzel said. “Temporary pets that you keep for a while and then they wander off.”
By conducting missions to minimoons and other near-Earth asteroids in their vicinity, NASA and other space agencies can test their technologies’ effectiveness in deep space, including life support systems, engines and propulsion systems, Paul Abell, chief scientist for small body exploration at NASA, told Live Science.
“Going to Mars is a big, big step,” he said. “There’s a lot of things that have to happen, so why don’t we look at some of these near-Earth asteroids that are in between the Earth-moon system and Mars.”
Minimoon journeys can assist scientists in their search for water on Mars, which is crucial for hydration and for creating additional rocket fuel. Liquid hydrogen is the preferred fuel for rockets and will be required to travel the more than 140 million miles (225 million km) from Earth to Mars. Currently, spacecraft have to carry all the water and fuel they need from Earth, which increases the payload weight and the amount of propellant required to break free from Earth’s gravitational pull, according to the “tyranny of the rocket equation.”
Essentially, if NASA increases the payload mass of a spacecraft even slightly, they have to add much more fuel to get it off the ground and into orbit — and the fuel itself adds even more weight to lift, creating a vicious cycle. The key to breaking this cycle is finding a way to refuel in space, Abell said.
“When you go on vacation, when you fly or drive anywhere, you’re not taking all your oxygen, all your food, everything with you for the entire round trip,” Abell said. “Well, it’s the same type of thing. We want to get away from having to take everything with us from Earth, all the way out and then come back, because that’s super expensive.”
The good news? Near-Earth asteroids may be ideal candidates for space gas stations. A growing body of research shows that many near-Earth asteroids are rich in minerals and water that’s locked inside the rock. If this water can be accessed, it could be split into hydrogen and oxygen, both key elements for creating rocket fuel.
“If you can access that water and leverage it, all of a sudden you have water to drink, you have oxygen to breathe and, more importantly, you have rocket fuel,” Abell said.
NASA is currently focused on extracting water from the moon, but several private companies such as Karman+, TransAstra, and AstroForge are eyeing asteroids for mining water and metals.
These operations are yet to commence due to the high costs and advanced technology required to reach these rocks. However, mini-moon missions can serve as a training ground for testing the feasibility of asteroid mining technologies for future commercial applications, as per a 2018 study.
However, minimoons themselves may not be the best option for fueling up spacecrafts because they are small, with surfaces dried out from “sitting in the sun, cooking for a long time,” said Binzel.
Robert Jedicke, an astronomer from the University of Hawaii and the author of a 2018 study, believes that many minimoons do not contain water due to their origin, which could be either breaking off from the Moon or getting pulled in from the edge of the main asteroid belt. These factors suggest a low potential for water. However, some scientists, including Abell, think that water may exist on these minimoons. Binzel, on the other hand, is optimistic and believes that there is a lot of uncertainty in the modeling. He suggests that we won’t know for sure until we investigate.
Even if minimoons do not have water, they could still be useful for companies to test their spacecraft maneuvering abilities near an asteroid. Jedicke is currently working with TransAstra to develop techniques for mining water from asteroids.
Construction of the Vera C. Rubin Observatory in the Chilean Andes is near completion. This observatory will house the world’s largest digital camera, called the Legacy Survey of Space and Time. Starting in 2025, this camera will take 700 pictures every night for 10 years to catalog the solar system at a 6-terapixel level of precision. This will help scientists understand mysterious substances like dark matter and dark energy. Additionally, this approach could help astronomers detect a minimoon as often as every three months.
Another NASA instrument, called the NEO Surveyor, will launch in 2027. This infrared space telescope will detect asteroids from space and scan the sky every two weeks to characterize potentially hazardous asteroids and comets near Earth’s orbit. This telescope will primarily focus on detecting “planet-killer asteroids,” but it has the potential to uncover small minimoons.
Scientists believe that studying near-Earth asteroids and minimoons could provide crucial clues about the mysteries of our solar system. Many scientists think that near-Earth asteroids brought the seeds of life to Earth early in our planet’s history. For tracing the chemical origins of the solar system and finding the ingredients that made life on Earth, minimoons are a great place to go.
“But the reason we haven’t gone to them before is there aren’t very many of them,” Binzel said. “We’re just now discovering them. But they will come to the forefront because we have new telescopes coming online.”