Asteroid Day 2024: A Plethora of New Insights

116 years ago today, in the taiga of the Yeniseysk Governorate, Russia, an unthinkable event occurred. In the early morning hours and without any warning, a gigantic explosion occurred deep in the woods, flattening tens of millions of trees in an area over eight hundred square miles, and potentially killing 3 residents of a nearby rural town. This bizarre occurrence was named the Tunguska Event, after the nearby Podkamennaya Tunguska River. 

The cause of the event, which was at least 200 times more powerful than the bomb dropped on Hiroshima, was a mystery for a very long time. However, with our modern understanding and based on written eye-witness accounts of the event, it is considered most likely that the Tunguska Event was the result of a large asteroid, or potentially a comet, exploding high in the air before reaching the ground.

It is because of this modern understanding of the event, and the potential threat it represents, that June 30th is “Asteroid Day,” described as a UN-sanctioned global awareness campaign. The event is organised to raise awareness on the importance of asteroid research, especially in regards to planetary protection. More information on specific Asteroid Day events, such as a live show to be hosted from Luxembourg can be found on the official Asteroid Day website.

For Asteroid Day 2024, we’ll be briefly covering updates to various small body missions.

Lookback at Lucy

Back on November 1st 2023, NASA’s Lucy mission had its first asteroid encounter of several yet to come with the small main-belt asteroid 152830 Dinkinesh. Dinkinesh was a late addition to Lucy’s roster, which delighted scientists with Lucy’s surprise discovery of Dinkinesh’s previously unknown small satellite, now named Selam. Shortly following the release of Space Scout’s previous article focusing on the Lucy mission, new imagery was released from a different angle and revealed newly found Selam was hiding its own surprise – Selam was a contact binary.

Contact binaries, when referring to asteroids, are asteroids formed of two distinct units once believed to be separate. Depending on the specific body, these units can be heavily weathered and only barely distinct, as is suspected to be the case with asteroid Itakowa, the target of JAXA’s Hayabusa mission. Selam however has two very distinct lobes, with a notable division between them. Selam represents what were once two separated moons of Dinkinesh that eventually became stuck together, and due to this nature models of the Dinkinesh-Selam system’s history are yielding new insights into the dynamism of the asteroid belt. 

It has long been suspected that the heating and cooling of asteroids due to solar energy can change their direction and rotation. Asteroids are warmed by the sun, and their complex shapes cause this energy to be radiated back into space unevenly, resulting in a low energy yet constant “thrust” bias in a certain direction. This is called the Yarkovsky–O’Keefe–Radzievskii–Paddack effect (or YORP effect), and some suspect that given enough time the YORP effect can cause asteroids to spin fast enough to shed material, providing an origin for many natural satellites of small asteroids. 

One paper, published in the Édition Diffusion Presse Sciences, purports that based on models of such an origin for Selam suggests that the small moon may have split off from Dinkinesh as recently as 1 million years ago–the blink of an eye on planetary timescales. If the model is accurate, it suggests that the YORP effect causes small asteroids in the main belt to shed material and generate moons constantly, explaining both the quantity of asteroid moons and potentially explains the origin of mysterious main-belt comets (small bodies in the main asteroid belt that host cometary tails).

Lucy will be flying by Earth on December 13th, 2024. This will be the mission’s final gravity assist prior to heading towards the Jupiter Trojan Asteroid Camps which are the mission’s primary targets. On its way to the outer solar system Lucy will visit another main belt asteroid, the much larger 52246 Donaldjohanson, in April of 2025.

Successes of OSIRIS-REx

Our previous coverage of OSIRIS-REx covered the mission’s return of samples from asteroid 101955 Bennu to Earth, an event which Space Scout team members attended. Since that story, NASA team members encountered and overcame issues opening the sample container. Due to complications with material leaking following the sample’s collection at Bennu, no measurements of the total sample mass were able to be taken before the return to Earth. Opening the sample container provided the first look at how successful OSIRIS-REx was.

The mission’s target was to return 60 grams of material from Bennu. The mission actually returned a total of 121.6 grams of material, just over double the target.

Now that the samples from Bennu are not only on Earth but accessible to researchers, the true science phase of the OSIRIS-REx mission is well underway. As explained by NASA Administrator Bill Nelson, “NASA missions like OSIRIS-REx will improve our understanding of asteroids that could threaten Earth while giving us a glimpse into what lies beyond. The sample has made it back to Earth, but there is still so much science to come – science like we’ve never seen before.”

Analysis of the samples quickly yielded intriguing results, confirming a high concentration of carbonaceous material, nitrogen, and water content. The sample material has been described as mirroring rocks found near Earth’s mid-ocean ridges, yielding tantalising clues into Bennu’s potentially dynamic origins. More recently, on June 26th 2024 it was announced that water-soluble phosphates, components of all known biochemistry, were discovered in the Bennu sample with a higher purity and larger grain size than observed in any other asteroid sample. The unprecedented discovery is a significant finding on the track to understanding how the conditions and chemistry that gives rise to life occur in the universe.

The OSIRIS-REx mission team has received several awards for the work done so far. The mission team received the National Space Club’s Dr. Robert H. Goddard Memorial Trophy, the National Aeronautic Association’s Robert J. Collier Trophy, and the American Astronomical Society’s Neil Armstrong Space Flight Achievement Award.

While the OSIRIS-REx mission lives on in laboratories on the ground, the spacecraft carries on operations under its new name, OSIRIS-APEX. OSIRIS-APEX aims to explore the infamous asteroid Apophis, which finds itself as an increasingly demanded target, which will encounter Earth in 2029.

Heraldling Hera

Looking ahead to the latter half of 2024, another asteroid mission is set to launch in October. Launching on a SpaceX Falcon 9 Block 5 will be the European Hera mission, a follow up to the previously launched American DART mission. DART, the Double Asteroid Redirection Test, was an impactor launched in 2021, which impacted Dimorphos, the satellite of larger asteroid Didymos in September of 2022. The purpose of the demonstration was to test whether the orbit of an asteroid could be changed via a small, fast moving impactor, and successfully shortened the orbital period of Dimorphos around Didymos by 32 minutes.

Hera’s mission in the Didymos System will be very different from DART’s, its time will be spent investigating the geology and composition of both asteroids, and the manners in which DART changed the system, particularly Dimorphos. Hera will also be the first spacecraft to enter orbit of and perform prolonged proximity observations of a double asteroid system while testing new autonomous guidance technologies. 

Hera features a suite of cameras across a variety of different wavelengths to determine the precise shape, sizes, composition, and roughness of both asteroids. The spacecraft will analyse both the qualities of the asteroids that may have affected DART’s redirection and also aspects that may be relevant to future ambitions to utilise asteroids as a source of valuable resources.

Hera will be joined by two cube satellites, which will deploy from the primary spacecraft after arrival in the Didymos System. The first is Juventas, which will carry the smallest radar ever flown in space, a gravimeter, a LIDAR system, visible light camera, and accelerometers. The second is Milani, which will carry a multispectral instrument, a dust instrument, and like its twin, a LIDAR instrument and visible light camera. Both spacecraft will focus their studies on Dimorphos, and end with soft landings on the small satellite asteroid. Hera’s mission will culminate in a similar fashion, with the spacecraft performing a soft landing on Didymos’ surface.

Hera is fully assembled, and both cubesats are integrated. Hera is currently finishing up preflight testing at ESA’s European Space Research and Technology Centre (ESTEC). After testing is completed, the spacecraft will be packaged up and shipped across the ocean to Cape Canaveral ahead of integration and launch in October.

In Closing

Asteroid Day is a day of awareness and appreciation for asteroid research, and the three missions discussed here today are only a fraction of the spacecraft (both flying and yet to launch) which aim to explore asteroid targets. Spacecraft are themselves only a small portion of the ways scientists study asteroids, ground observations and meteorite research are also vital pieces of the puzzle.  NASA/JPL’s Solar System Dynamics website lists that there are 1,375,291 asteroids known to exist in our solar system today (counting dwarf planets and Kuiper Belt Objects). Asteroids are the most numerous class of planetary bodies in the solar system, and they have a great bounty of knowledge to teach us, represent potential threats to our planet, and even potential opportunities.

This Asteroid Day, we encourage you to look up, and even if you can’t see them, remember that they are there.