Wendy K. Caldwell is a mathematician / planetary scientist at Los Alamos National Laboratory. She is the lead author of Los Alamos National Laboratory’s Psyche Research and a member of the DART Investigation Team, a multi-agency international collaboration. She is also a regular person who volunteers her time, acting, dancing, governing and choreographing for local performance organizations. Caldwell contributed to this article Space.com’s Expert Voices: Op-Ed & Insights.
This summer, NASA launched its first mission on a metallic asteroid, 16 Psyche, in the main sequence. Asteroid belt between the orbits of Mars and Jupiter. Previous missions have explored rocks and icy asteroids, but the psyche’s composition is generally believed to consist of a considerable amount of metal. Of course, in today’s click-bait culture, Psyche googles you into that linguistic internet rabbit hole of stories about how it’s worth more than the world economy. As tempting as this idea is, we will not scrap it and sell it for parts.
From a scientific perspective, however, psyche is invaluable.
The Psyche Mission: Visit a Metal Asteroid
At school we learn that Earth has a layer structure: crust, mantle and core (inside and outside). Billions of years ago, when the Earth and other planets formed, collisions between solid bodies were more common than today. Some of these collisions have led to accretion, helping to build up these layers and lead to larger solid bodies that become planets. Others led to disturbances, in which planetesimals were blown apart before they could completely form planets. Metallic asteroids are thought to be their remnants, cores of planets that have been released from their outer layers by high-velocity impacts.
Psyche is the largest of these remains, with a diameter of about 140 miles (225 kilometers). The psyche can hold answers to questions about the early solar system, even as planets form, or, in the psyche’s case, not fully form. The NASA mission will be equipped with tools to measure various properties of the psyche, and these data can provide more insights into the composition of the asteroid, including how much of it is metallic and how much porosity (empty space) is present.
The mission is not expected to reach the asteroid until 2026. Until it begins to collect data, computational models can help us understand the psyche by exploring the feasibility of different material compositions for it. Psyche has two major impact structures on its southern hemisphere. Simulating the formation of these craters with computational models helps to investigate how such large and relatively flat craters can be formed on psyche. Simulations we have used with the Los Alamos National Laboratory’s extensive computational resources show that psyche can be a garlic-pile configuration, consisting of large boulders held together by gravitational forces. In our simulations, effects and landfill create crater shapes similar to those found on psyche: large diameter, relatively flat and deep. (Watch simulation video hey).
At Los Alamos we are interested in solid bodies for another application: planetary defense. If a large body were on an Earth-crossing trajectory, the more we knew about the object, the greater the likelihood of successful rejection attempts to avoid a catastrophic impact. Perhaps the most famous event was the Chicxulub Impact, which the dinosaurs deleted. From that time, about 65 million to 66 million years ago, the Earth’s environment changed forever.
Before panicking, note that the frequency of such catastrophic impacts varies from tens of thousands to hundreds of millions of years. To clarify, Psyche is not on a cross-country route and does not pose a threat. Data from the Psyche mission, however, can give us a better idea of how well our observation and modeling tools determine the material properties of distant objects. Such information would be crucial to successfully dispose of any potentially dangerous objects in the future.
These objects are characterized as large enough to pose a danger – about 99 feet (30 meters) above, for a city, and about 460 feet (140 meters) above, for a region – and on a path for within 4.6 million Miles to come (7.4 million km) from Earth’s orbit. The notion of “close” in space is very different from that here on earth. An object that is viewed after the Earth’s orbit is approximately the distance that the Earth travels in space in three days. So, when you hear of a close approach, the object is often still extremely far away and often too small to pose a threat, largely thanks to the Earth’s atmosphere, which offers an extra layer of protection against incoming objects.
Coherence: Potentially dangerous asteroids (pictures)
At the moment, an ongoing planetary defense mission may hold the answers to the question of whether we can launch an asteroid with a kinetic impactor – essentially a large cannonball. NASA’s Double Asteroid Redirection Test (DART) mission, Launched November 2021, will travel into the Didymos binary star asteroid system, in which a smaller body, Dimorphos, orbits the larger Didymos. Like the psyche, Dimorphos is far away, which limits the Earth-based observations of its material properties. Furthermore, like psyche, Dimorphos poses no danger to Earth.
The spacecraft will affect Dimorphos at speeds of more than 13,320 mph (21,440 kmph), and the subsequent transfer of energy is expected to change the asteroid’s orbit. The data are collected before, during and after the impact, and this data is used for the efficiency of the kinetic impactor method for planetary defense.
We currently use the same modeling techniques we used to understand psyche to model impact on Dimorphos. Of course, there are some notable differences. Dimorphos, which has a diameter of about 558 feet (170 m), is significantly smaller than Psyche. As a result, Dimorphos can be modeled in more detail than Psyche, based on the computational cost of large simulations. We modeled Psyche with the nickel-iron alloy Monel, based on the properties of the ore from the Sudbury impact crater in Canada. The ore is thought to have come from the impactor that formed the crater, which means that the monel is essentially “celestial metal”, which probably has similar properties to metallic asteroids.
Dimorphos, on the other hand, is a rock body, so we use igneous geological materials like basalt, which has similar properties as moon samples, in our models. Because those DART Mission Years of planning, we know exactly what the spacecraft impactor is: we know size, shape, material, speed and a range of likely impact angles. Thus, Dimorphos models can be more finely tuned to represent the current impact. The impact on the psyche was billions of years ago, so model choices were harder to make.
The good news is that both of these missions result in additional data that we can use to update our models for more accurate results in the future. The data also help us to determine the uncertainties of our models and could mark areas in which we can reduce these uncertainties. Science is never finished: we are always re-evaluating our methods, conducting new experiments, collecting new data and forming new hypotheses for testing. But science is getting better: new information leads to more accurate models, falsifies some hypotheses, and shows that others align with our current understanding of the field. Even a discovery like “that did not work at all” has great scientific value. Knowing what is not working can point us in the right direction for what is working.
When the Psyche mission launches this summer, and when the DART spaceship crashes in Dimorphos this fall, be sure to grab a glass of science. 2022 will be the most exciting year for planetary science since I entered the field as a graduate. For the first time ever, a mission will begin a journey into the main asteroid belt to visit a metallic asteroid, potentially a window to the early days of the solar system. Shortly after the launch of this mission, the DART spaceship Dimorphos will embark on a single voyage to an epic crash that could pave the way for a new era in planetary defense. Science is about trial and error, and even though we do not always get it right, we never stop trying.
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