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How the Sun Affects Asteroids in Our Neighborhood

It’s no secret the Sun affects us here on Earth in countless ways, from causing sunburns to helping our houseplants thrive. The Sun affects other objects in space, too, like asteroids! It can keep them in place. It can move them. And it can even shape them.

Asteroids embody the story of our solar system’s beginning. Jupiter’s Trojan asteroids, which orbit the Sun on the same path as the gas giant, are no exception. The Trojans are thought to be left over from the objects that eventually formed our planets, and studying them might offer clues about how the solar system came to be.

Over the next 12 years, NASA’s Lucy mission will visit eight asteroids—including seven Trojans— to help answer big questions about planet formation and the origins of our solar system. It will take the spacecraft about 3.5 years to reach its first destination.

How does the Sun affect what Lucy might find?

Place in Space

Credits: Astronomical Institute of CAS/Petr Scheirich

The Sun makes up 99.8% of the solar system’s mass and exerts a strong gravitational force as a result. In the case of the Trojan asteroids that Lucy will visit, their very location in space is dictated in part by the Sun’s gravity. They are clustered at two Lagrange points. These are locations where the gravitational forces of two massive objects—in this case the Sun and Jupiter—are balanced in such a way that smaller objects (like asteroids or satellites) stay put relative to the larger bodies. The Trojans lead and follow Jupiter in its orbit by 60° at Lagrange points L4 and L5.

Pushing Asteroids Around (with Light!)

The Sun can move and spin asteroids with light! Like many objects in space, asteroids rotate. At any given moment, the Sun-facing side of an asteroid absorbs sunlight while the dark side sheds energy as heat. When the heat escapes, it creates an infinitesimal amount of thrust, pushing the asteroid ever so slightly and altering its rotational rate. The Trojans are farther from the Sun than other asteroids we’ve studied before, and it remains to be seen how sunlight affects their movement.

Cracking the Surface (Also with Light!)

The Sun can break asteroids, too. Rocks expand as they warm and contract when they cool. This repeated fluctuation can cause them to crack. The phenomenon is more intense for objects without atmospheres, such as asteroids, where temperatures vary wildly. Therefore, even though the Trojans are farther from the Sun than rocks on Earth, they’ll likely show more signs of thermal fracturing.

Solar Wind-Swept

Like everything in our solar system, asteroids are battered by the solar wind, a steady stream of particles, magnetic fields, and radiation that flows from the Sun. For the most part, Earth’s magnetic field protects us from this bombardment. Without magnetic fields or atmospheres of their own, asteroids receive the brunt of the solar wind. When incoming particles strike an asteroid, they can kick some material off into space, changing the fundamental chemistry of what’s left behind.

Follow along with Lucy’s journey with NASA Solar System on Instagram, Facebook, and Twitter, and be sure to tune in for the launch at 5 a.m. EDT (09:00 UTC) on Saturday, Oct. 16 at nasa.gov/live.

Make sure to follow us on Tumblr for your regular dose of space!

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