In a surprise Planetary Pandemonium episode, we look at a comet that is caught in the process of moving from Centaur to Jupiter Family Comet and doing it on a human timescale. Also, an ancient Martian megaflood and a newly discovered minimoon for Earth.


This is the Daily Space for today, Friday, November 24, 2020. I am your host, Beth Johnson, and I am here to put planetary science in your brain.

I hope all of our friends in the U.S. had a lovely Thanksgiving, under the circumstances. I personally enjoyed dinner with my husband, son, and our best friend. I baked pumpkin pies, and we had prime rib and all the sides. Then we watched cheesy Christmas romance movies because we all need some happiness and cheer.

So to those of you taking the time to tune in today, we thank you. Pamela has said it a few times this week, but I want to express my own thanks for all your support and kindness. Thank you.

Now, for the planetary news of the week.

Our first story of the day comes from our very own Planetary Science Institute, and it is fresh off the press release list. For once, we’re going to talk about the science behind a comet and not just whether or not it will become a naked-eye wonder.

IMAGE: Comet 2019 LD2 (ATLAS) as seen by the Hubble Space Telescope. CREDIT: Hubble Space Telescope/Bryce Bolin.

Let’s start with some background information. When I was working as an intern, I learned that there were basically two types of comets: long-period comets and Jupiter Family comets. Long-period comets orbit the Sun on a scale of 200 or more years. Jupiter Family comets orbit the Sun from inside the orbit of Jupiter. Then I learned there were also short-period comets that orbit from the Kuiper Belt inward to Jupiter.

There’s another type of object that somewhat falls into the cometary category, however. They’re called Centaurs. The press release explains: Centaurs are icy bodies in unstable orbits between Jupiter and Neptune, and cross the orbits of one or more of the giant planets in their journey around the Sun; the gravity of these planets provide rapid dynamical evolution of the objects, and either eject them from the solar system entirely or cause them to eventually evolve inward of Jupiter, to become Jupiter Family Comets. Prior to this migration, Centaurs began as objects beyond the orbit of Neptune (trans-Neptunian Objects), whose gravitational tugs causes the object to slowly leak into the Centaur population; this entire migration from beyond Neptune to JFC lasts a few million to a few tens of millions of years.

And here is where today’s press release gets interesting: observers using the ATLAS telescopes found Comet 2019 LD2 last year, and it is in the process of transitioning from a Centaur into a Jupiter Family comet, a process we have never witnessed before. Lead author Jordan Steckloff says: We find that 2019 LD2 is currently in the vicinity of a dynamical ‘Gateway’ that facilitates the majority of transitions from the Centaur population into the Jupiter Family of Comets. The dynamical gateway is a region beyond Jupiter, extending to just inside of Saturn’s influence.

Steckloff goes on to state: Most significantly, our work found that LD2 is most likely a pristine comet. Although it has likely lost some supervolatile ices such as carbon dioxide ice in the Outer Solar System beyond Jupiter, it is unlikely to have ever been in the inner Solar System, which is warm enough for water ice to [sublimate]. This means that LD2 is a pristine comet, and presents a unique opportunity to observe how pristine JFCs behave as their water ice begins to sublime for the first time and drive comet activity. Moreover, this transition is likely to finish in only 40 years from now, which is a blink of an eye for astronomy. This means that people alive today will be able to follow this object all the way through its transition into the JFC population.

Forty years! Astronomical events usually happen on astronomical timescales, but I might even still be alive to see that transition finish, which is amazing. This research on this one small body might help answer important questions about solar system evolution, such as why there are active comets and inactive asteroids and how they change definition. Planetary scientists love to categorize objects, and we need to understand the categories fully and the bodies we place within those boxes.

This article was published in Astrophysical Journal Letters and is very interesting to me. We’re hoping to have Dr. Steckloff on the Daily Space next week, so please stay tuned!

Slightly closer to home, Mars is making news again. I mean, when isn’t Mars making news these days? This time, field geologists have analyzed data taken from Curiosity at Gale Crater and determined that a megaflood occurred in ancient Martian history.

IMAGE: This composite, false-color image of Mount Sharp inside Gale crater on Mars shows geologists a changing planetary environment. On Mars, the sky is not blue, but the image was made to resemble Earth so that scientists could distinguish stratification layers. CREDIT: NASA/JPL

In a paper published in Nature Scientific Reports, researchers explain how this megaflood left behind familiar ripple structures in the crater that match ones we have on Earth. The flood was likely set off by a large meteor impact four billion years ago that unleashed massive amounts of ice stored in the subsurface of the red planet.

According to lead author Ezat Heydari: This case includes the occurrence of giant wave-shaped features in sedimentary layers of Gale crater, often called “megaripples” or antidunes that are about 30-feet high and spaced about 450 feet apart.

These features match antidunes formed by melting ice here on Earth around two million years ago. Per the press release: The most likely cause of the Mars flooding was the melting of ice from heat generated by a large impact, which released carbon dioxide and methane from the planet’s frozen reservoirs. The water vapor and release of gases combined to produce a short period of warm and wet conditions on the red planet.

Condensation formed water vapor clouds, which in turn created torrential rain, possibly planetwide. That water entered Gale Crater, then combined with water coming down from Mount Sharp to produce gigantic flash floods.

It’s generally accepted that Mars had water in the past, and that has led a lot of us to think life was once possible. All we can really do now is wait for Perseverance to arrive and see if it finds what we’re hoping for: evidence of that past life.

From Mars, we move even closer to home and take a look at Earth’s latest minimoon, a newly discovered asteroid with the designation 2020 CD3. Astronomers used the Lowell Discovery Telescope to analyze this second minimoon, and their work is published in The Astronomical Journal.

IMAGE: International Gemini Observatory image of 2020 CD3 (center, point source) obtained with the 8-meter Gemini North telescope on Hawaii’s Maunakea. The image combines three images each obtained using different filters to produce this color composite. 2020 CD3 remains stationary in the image since it was being tracked by the telescope as it appears to move relative to the background stars, which appear trailed due to the object’s motion. CREDIT: International Gemini Observatory/NOIRLab/NSF/AURA/G. Fedorets

A minimoon is a tiny asteroid that gets captured by Earth’s gravity, orbits our planet for a while, and then gets flung back out into the solar system. The first minimoon discovered here was found back in 2006.

CD3 was discovered early this year, and scientists quickly rallied to observe and understand our new satellite while they had the chance. Measurements indicate that CD3 is a natural satellite, made of silicate, about 1-1.5 meters in diameter and that it came within about 13,000 kilometers of Earth.

While this is only the second minimoon found, the expectation in the astronomical community is that we will find more of these small, transient bodies once the Rubin Observatory is complete. Again, understanding minimoons will help understand the evolution of our solar system and possibly even provide targets for robotic exploration. That sounds really cool to me, y’all.

This has been the Daily Space.

Learn More

Comet 2019 LD2 (ATLAS) Found to Be Actively Transitioning

Field Geology at Mars’s Equator Points to Ancient Megaflood

Scientists Help Characterize Earth’s Second Known Minimoon


Written by Beth Johnson
Hosted by Beth Johnson
Audio and Video Editing by Ally Pelphrey
Content Editing by Beth Johnson
Executive Producer is Dr. Pamela Gay
Intro and Outro music by Kevin MacLeod,