Pluto and its lovely moon
Earth’s moon formed after a huge object crashed into the planet, sending debris out into space that got caught in Earth’s orbit and eventually became the moon we know today.
Astronomers thought this is how Pluto managed to collect its large moon Charon. But now, new research finds that moon’s story may have been much calmer.
The gentler method is known as the “kiss and capture” method” where Pluto and its large moon gently collided, resulting in Charon staying in the small dwarf planet’s orbit.
Adeene Denton, a NASA postdoctoral program fellow, said the strangest thing about Charon is its size. The moon is about half the size of Pluto, the dwarf planet it orbits.
“That's pretty unusual,” Denton said. “Because if we look at other solar system moons like say, Phobos and Deimos that are the two moons of Mars, they're a small fraction of a percent the mass of Mars--So the only other comparison point we really have is our moon, which is also weirdly large in comparison to the Earth.”
Now, the “kiss and capture” method reflects the idea that Pluto and its moon Charon quickly and briefly merged and then separated. Moreover, that separation led Charon to being captured in Pluto’s orbit.
“It's a relatively gentle collision at around one kilometer (0.61 miles) per second,” Denton said. “Fighter jets travel faster than that. It's not very fast. It's actually, on a planetary scale, quite gentle--So even though a giant impact is the source, the actual process by which Charon gets captured as a moon is very different from how the Earth captures its moon.”
While her research on Charon was just published, Denton has had a fascination with Pluto for about a decade, especially after NASA’s New Horizons mission visited the dwarf planet in 2015.
“Everybody was worried that we were going to fly by Pluto, and it was going to be this dead world,” Denton said “But instead, it had so many things going on. I was just absolutely captivated by everything that I saw there: Pluto's heart, its mountains, its glaciers. I wanted to know how it all works.”
Uncovering the secrets of Chiron
Chiron is a small object known as a centaur that orbits the Sun in the outer solar system, near the giant planets like Jupiter and Neptune.
Centaurs are icy and come from the Kuiper Belt, and their orbits are unstable as they move between the outer planets. Scientists have observed that Chiron shows comet-like activity, including a faint cloud of gas and dust around it, called a coma.
Recently, scientists have focused on examining the surface of Chiron, hoping to uncover its composition. Using spectroscopy, scientists can analyze the reflected light at various wavelengths to determine the materials on the surface.
Noemi Pinilla-Alonso, a professor at the Institute for Space Science and Technologies in Asturias said they, “found absorption bands that indicate ice is on the surface, but we also found emission bands that indicate that it is active.”
She further explained that the methane on Chiron isn’t sitting on the surface as ice, but it is trapped in layers just below it. When sunlight warms Chiron, the heat penetrates the surface and reaches these underground layers, releasing methane gas through cracks. That’s why we see methane gas, but not methane ice on the surface.
Charles Schambeau, a research assistant professor at the University of Central Florida said, “Based on the closeness to Chiron to the sun gives us the temperature on the surface. We know that…the surface is way too hot for carbon monoxide to survive.”
An intriguing aspect of Chiron is its proximity to the Sun, where carbon dioxide is usually too hot to remain on the surface. However, based on these findings, it appears to be surviving in this environment.
Over the past two years, scientists have been using the James Webb Space Telescope for different projects in planetary science. While progress has been made, scientists are still just beginning to answer some of the biggest questions.
Schambeau said, “Chiron helps us understand where's our placement….what other solar systems that we see forming have similar characteristics to ours, that could potentially provide the ultimate question of that solar system that we're observing.”
