Enlarge / An artist's illustration of NASA's two Janus spacecraft as they would have appeared in space. (credit: Lockheed Martin )

Two small spacecraft should have now been cruising through the Solar System on the way to study unexplored asteroids, but after several years of development and nearly $50 million in expenditures, NASA announced Tuesday the probes will remain locked inside a Lockheed Martin factory in Colorado.

That’s because the mission, called Janus, was supposed to launch last year as a piggyback payload on the same rocket with NASA’s much larger Psyche spacecraft , which will fly to a 140-mile-wide (225-kilometer) metal-rich asteroid—also named Psyche—for more than two years of close-up observations. Problems with software testing on the Psyche spacecraft prompted NASA managers to delay the launch by more than a year.

An independent review board set up to analyze the reasons for the Psyche launch delay identified issues with the spacecraft’s software and weaknesses in the plan to test the software before Psyche’s launch. Digging deeper, the review panel determined that NASA’s Jet Propulsion Laboratory, which manages the Psyche mission, was encumbered by staffing and workforce problems exacerbated by the COVID-19 pandemic.

Enlarge / Artist’s illustration shows the ejection of a cloud of debris after NASA’s DART spacecraft collided with the asteroid Dimorphos. (credit: ESO/M. Kornmesser)

Last September, the Double Asteroid Redirect Test, or DART, smashed a spacecraft into a small binary asteroid called Dimorphos, successfully altering its orbit around a larger companion. We're now learning more about the aftermath of that collision, thanks to two new papers reporting on data collected by the European Southern Observatory's Very Large Telescope . The first, published in the journal Astronomy and Astrophysics, examined the debris from the collision to learn more about the asteroid's composition. The second, published in the Astrophysical Journal Letters, reported on how the impact changed the asteroid's surface.

As we've reported previously , Dimorphos is less than 200 meters across and cannot be resolved from Earth. Instead, the binary asteroid looks like a single object from here, with most of the light reflecting off the far larger Didymos. What we can see, however, is that the Didymos system sporadically darkens. Most of the time, the two asteroids are arranged so that Earth receives light reflected off both. But Dimorphos' orbit sporadically takes it behind Didymos from Earth's perspective, meaning that we only receive light reflected off one of the two bodies—this causes the darkening. By measuring the darkening's time periods, we can work out how long it takes Dimorphos to orbit and thus how far apart the two asteroids are.

Before DART, Dimorphos' orbit took 11 hours and 55 minutes; post-impact, it's down to 11 hours and 23 minutes. For those averse to math, that's 32 minutes shorter (about 4 percent). NASA estimates that the orbit is now "tens of meters" closer to Didymos. This orbital shift was confirmed by radar imaging. Earlier this month , Nature published five papers that collectively reconstructed the impact and its aftermath to explain how DART's collision had an outsize effect. Those results indicated that impactors like DART could be a viable means of protecting the planet from small asteroids.

Despite its distance from the Sun, the asteroid belt will disintegrate as it expands. (credit: NASA/ESA/STScI )

We tend to view the bodies of the Solar System as creations of gravity, which pulled their parts together and hold them in place as they orbit. But as we saw with ideas about the formation of Arrokoth , there are lots of situations where gravity is essentially a constant for long periods of time. And given enough of that time, relatively small forces like friction from sparse gas clouds or pressure from the light of the Sun can add up and create dramatic changes. In fact, a remarkable number of these potential influences have been identified and simulated.

One of these has been named the YORP effect, for its developers, Yarkovsky, O'Keefe, Radzievskii, and Paddack. It describes how light can alter the rotational properties of orbiting bodies. In a recent edition of the Monthly Notices of the Royal Astronomical Society, Dimitri Veras and Daniel Scheeres decided to calculate what happens as the Sun ages, the intensity of its light increases dramatically, and the entire asteroid belt gets YORPed.

A (perhaps too) bright future

It's pretty widely understood that, as the Sun ages, it will expand until its outer edges come close to the Earth's orbit. What's less widely recognized is that it will get quite a lot brighter than it is at present. Other stars with masses similar to the Sun can get thousands of times brighter than the Sun in the last stages of their fusion-driven lives, allowing effects that might otherwise be a bit weak to become dominant.

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