Universe Today
Last year, astronomers detected the Near-Earth Asteroid (NEA) 2024 YR4 that orbits the Sun every four years and periodically crosses Earth's orbit. The nature of its orbit makes it a Potentially Hazardous Object (PHO), meaning it could pose a collision risk with Earth someday. Recently, refined estimates of its orbit have ruled out the possibility that it will strike Earth in 2032. Nevertheless, there will likely be further close encounters with Earth well into the distant future.
This also presents opportunities for a close flyby mission to study YR4 up close, thus providing insight into the early Solar System. In a recent paper, Adam Hibberd and Marshall Eubanks explore the feasibility of various mission architectures. The mission could encounter the asteroid as early as 2028, but multiple launch windows are identified. This mission could also conduct a sample return, complementing the Hayabusa I and I, OSIRIS-REx missions, and future attempts to explore NEAs.
Adam Hibberd is a software and research engineer in Astronautics with the Initiative for Interstellar Studies (i4is) and the owner/director of Hibberd Astronautics Ltd. T. Marshall Eubanks is the Chief Scientist at Space Initiatives Inc. and the CEO of Asteroid Initiatives LLC. The draft version of their paper, "Preliminary Analysis into the Feasibility of Missions to Asteroid 2024 YR," recently appeared online and is being reviewed for publication in Acta Astronautica.
Asteroid YR4 was discovered on December 27th, 2024, by the Asteroid Terrestrial-impact Last Alert System (ATLAS), an early warning system developed by the University of Hawaii and funded by NASA. At the time, astronomers estimated it had a 1% chance of impacting Earth on December 22nd, 2032. By February, these estimates temporarily rose to 2.3% before refined measurements by major telescopes worldwide essentially reduced the estimates of an impact to zero.
Asteroids are essentially leftover material from the formation of the Solar System ca. 4.5 billion years ago. Therefore, studying these bodies can reveal tantalizing clues about how our system evolved and address major questions about how life emerged. This makes NEAs particularly interesting to scientists, as they are more easily reached than asteroids in the Main Belt or beyond. As Eubanks told Universe Today via email:
"Well, I personally doubt it's primordial. I suspect it is a piece of an asteroid, probably knocked out of an orbit at ~4.18 AU (its aphelion). Getting a good look at it might help characterize objects in the currently poorly explored range between 2.77 AU (Ceres, which had a long-term visit from Dawn) and 5.2 AU (where the Jupiter Trojans are, and where Lucy is going)."
Multiple sample returns have been conducted with NEAs in recent years, leading to some very interesting revelations. This includes JAXA's Hayabusa mission, which rendezvoused with the asteroid 25143 Itokawa in 2005, and Hayabusa2, which rendezvoused with 162173 Ryugu in 2018. Most recently, NASA's Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) obtained samples from asteroid 101955 Bennu.
In addition to confirming that S-type asteroids are the source of the most common type of meteorites, the Itokawa samples also revealed the presence of water and extraterrestrial mineral grains. Meanwhile, the Bennu samples revealed comet particles and 20 different types of amino acids. The OSIRIS-REx sample, the largest ever returned to Earth (in September 2023), contained organic compounds and hydrated minerals. These samples support the theory that asteroids and comets were responsible for delivering water and the building blocks of life to Earth billions of years ago.
However, what makes YR4 a good candidate for future missions goes beyond science. As Eubanks indicated, its status as a PHO also means it could help inform planetary defense strategies. "It is a potentially hazardous asteroid that may still hit the Moon in 2032, and even if it doesn't, it could certainly become an actual hazard in the future," he said. "Characterizing it is important both in case it becomes a future hazard and (as the NASA Planetary Decadal survey states) a useful exercise to teach us better how to inspect these bodies."
As part of their study, Eubanks and Hibberd explored various mission architectures that could rendezvous with YR4 up to and including its close encounter in 2032. This mission would exploit the software known as "Optimum Interplanetary Trajectory Software" (OITS) developed by Hibberd. As he described the development process and the purpose of the software via email:
"I developed OITS in my spare time as a challenge to myself to learn MATLAB [a programming and numeric computing platform to analyze data, develop algorithms, and create models]. OITS is a preliminary interplanetary mission design tool. For the paper in question, no gravity assists were modelled, though OITS does have the capability to simulate multiple gravity assists. The overarching aim is to solve what is known as the 'Lambert problem', many, many times."
As Hibberd described it, this problem applies to two known points in space (i.e., celestial bodies) that are separated by a time interval in the presence of a gravitational pull - in this case, the Sun. Ultimately, there are two orbits that connect these planets while respecting these conditions: the short way and the long way. If there are many celestial bodies in sequence ('N') at different times and positions (N), that makes many possible combinations of short ways and long ways a spacecraft can take (2 x N-1 times).
"My software finds the optimal trajectory in that it determines the time at each celestial body in turn that overall minimizes a metric known as 'DeltaV'," he added. "This metric 'DeltaV' is the overall velocity increment the spacecraft must deliver using its rocket engines. Minimizing this DeltaV results in MINIMUM TOTAL FUEL ONBOARD, in order that as much of the spacecraft mass can be dedicated to things like instrumentation or communications, or whatever is needed to realize the mission goals."
Hibberd has used OITS to create models for Project Lyra, another proposal he and Eubanks developed with researchers from the i4is to study the feasibility of missions to interstellar object 1I/'Oumuamua. Using this software, the two considered multiple mission architectures using the New Horizons spacecraft as a reference mission. Their investigation was not limited to this mission since they would require launches around late 2028 and early 2029 with much longer flight durations.
All told, said Hibberd, the architectures they considered fell into three categories, including:
Flyby: where they attempt to minimize the hyperbolic energy needed to escape Earth and reach the target (so it is as easy as possible for any launch vehicle to achieve escape).
Sample Return: where the time period of the trajectory to the target is a whole number of years to ensure the spacecraft will return to Earth later on in its 1-year orbit.
Rendezvous: where the spacecraft must match velocity with the target to stay with it as it orbits the Sun.
In addition, Eubanks explained how advancements in small satellite and gram-scale wafercraft could enable a low-cost mission that could fly as part of a larger mission:
"2024 YR4 presents us with an opportunity-rich environment, and one of the things that excites me here is that we could use small spacecraft - Cubesats or Disksats - to explore it. As a specific example, any CLPS or Artemis launch in mid-2028, for example, could potentially send a small nanospacecraft to YR4 in late December of that year (2028) using its lunar transfer orbit. Clearly, if we are going to routinely explore many of the PHA (and even prospect them for asteroid mining), this will have to be done with small spacecraft, and YR4 provides an opportunity to begin this process."
The study of asteroids is a growing field, with missions to NEAs paralleled by the study of populations in the Main Belt and outer Solar System. In the coming years, missions to interstellar objects (ISOs) could also be realized. The results of their investigations could not only expand our knowledge of the Solar System and how extrasolar star systems have evolved with time.
Further Reading: arXiv