Planetary formation made the news in three different ways this week. Find out how surprising results from studies of a meteorite, a debris field and the planet Venus all shed new light on our own planet’s deep history.
Back in public school, everyone in my class had an oversized atlas in our desks with a blue-black cover. On the cover was a map of our solar system, from the Sun all the way out to Pluto, tracing the elliptical orbit of each planet in light blue.
The world was caught up in the Space Race at the time, and planets were a hot topic. TV shows like Star Trek and Lost in Space reinforced our youthful fascination with worlds beyond Earth.
We take the existence of other planets for granted in the 21st century. We say things like, “he looked at me as if I was from another planet” as if we know what people from other planets are like.
Astronomers Have Now Discovered Over 5,000 Planets
Our matter-of-fact attitude isn’t surprising, since astronomers have now discovered over 5,000 planets in our galaxy. What’s remarkable is how little we know about how planets form.
Scientists call their most accepted theory on planetary formation the nebular hypothesis. The idea is that when stars form out of gas clouds, they’re surrounded by a disc-shaped cloud of debris. That debris seems to gradually clump together into planets like those in our solar system.
Planetary science was in the news several times this week. As usual in astronomy, to paraphrase J. B. S. Haldane, the findings were “not only queerer than we suppose, but queerer than we can suppose.”
Meteorite from the Interior of the Planet Mars
The journal Science published a study of the Chassigny Meteorite from the interior of the planet Mars. It landed in northeastern France in 1815.
Since it came from inside Mars, the team expected this vintage meteorite could tell them more about planetary formation in the case of the red planet. It did, but not in the way they expected.
The researchers used a new method developed at the University of California, Davis Noble Gas Laboratory to measure tiny amounts of krypton isotopes in the meteorite. They expected to confirm the krypton came from the solar nebula from which the solar system formed.
Thought Meteorite Would Come from Sun’s Nebula
They thought they’d get that result because a meteorite from inside Mars would be made of materials from the sun’s nebula. A meteorite from the surface would contain different isotopes of krypton deposited there by meteorites after the planet formed.
The experiment showed the opposite. The krypton they measured came, not from the solar nebula, but from early meteorites.
These results mean that meteorites were bringing krypton to Mars much earlier than scientists believed. It also means meteorites were colliding with the planet while the sun’s early nebula still existed, which is the opposite of what the researchers expected.
Results Were Opposite of what Researchers Expected
As Professor Sujoy Mukhopadhyay of the UC Davis Department of Earth and Planetary Sciences explained, “While our study clearly points to the chondritic gases in the Martian interior, it also raises some interesting questions about the origin and composition of Mars’ early atmosphere.”
Meanwhile, at a meeting of the American Astronomical Society (AAS) in Pasadena California, a different kind of planetary formation news story broke. The Astrophysical Journal Letters will be publishing another new study with equally unexpected results.
A team of researchers were using the international astronomy facility called the Atacama Large Millimeter/submillimeter Array (ALMA) to study the debris disk around a nearby star. This would be the first time astronomers could image such a disk with the precision of millimetre wavelengths.
Researchers Studying Debris Disk Around Nearby Star
The researchers expected to see a nearly face-on ring containing clumps of dust around the star they call HD 53143 . However, just like the team at UC Davis, they saw something completely different.
Instead of a nice, regular disk, they saw an odd-shaped, complicated field of debris surrounding the star. It’s the most unusual debris field astronomers have ever seen.
Meredith MacGregor is an associate professor at the Center for Astrophysics and Space Astronomy and at the Department of Astrophysical and Planetary Sciences at Colorado University, Boulder. She’s also the lead author of the second study.
“Had Never Seen such a Complicated Structure”
“Until now, scientists had never seen a debris disk with such a complicated structure. In addition to being an ellipse with a star at one focus, it also likely has a second inner disk that is misaligned or tilted relative to the outer disk,” Professor MacGregor explained. “In order to produce this structure, there must be a planet or planets in the system that are gravitationally perturbing the material in the disk.”
Professor MacGregor went on to explain why this misshapen debris disk is important to science. “Debris disks are the fossil record of planet formation, and this new result is confirmation that there is much more to be learned from these systems and that knowledge may provide a glimpse into the complicated dynamics of young star systems similar to our own Solar System.”
Also this week, the journal Nature Communications released another surprising planetary formation study. Scientists at the University of Cambridge were taking a closer look at the planet Venus.
Speculated There Could Be Life Forms in Venus’ Atmosphere
Over the past few decades, astrobiologists have speculated there could be life forms living in that planet’s unimaginably thick atmosphere. Since all living things consume some kind of food and expel the resulting waste, the Cambridge team tried to find evidence of this in the Venusian atmosphere.
“We looked at the sulphur-based ‘food’ available in the Venusian atmosphere – it’s not anything you or I would want to eat, but it is the main available energy source,” the paper’s lead author Professor Sean Jordan from Cambridge’s Institute of Astronomy explains. “If that food is being consumed by life, we should see evidence of that through specific chemicals being lost and gained in the atmosphere.”
Professor Jordan came up with a list of the kinds of metabolic reactions we’d expect to see if life existed in Venus’ sulphur (S02)-rich atmosphere. Then, they came up with atmospheric and biochemical models to represent these reactions.
Life in Venus’ Clouds Couldn’t Explain Chemistry
When they ran their models, they found that life in the clouds couldn’t explain the atmospheric chemistry on Venus. “We wanted life to be a potential explanation, but when we ran the models, it isn’t a viable solution,” explained Professor Jordan. “But if life isn’t responsible for what we see on Venus, it’s still a problem to be solved – there’s lots of strange chemistry to follow up on.”
If every experiment turned out exactly as planned, science would be awfully dull. Scientists agree that there’s no such thing as a “failed experiment” because we learn from every result including, and maybe especially, the ones that yield unexpected results.
All three of these planetary formation studies have shed new light on the New Story we all need to learn about where planets like Earth come from and how life arose here. To understand the world around us and our place in it, we need to follow the evidence where it leads, even when that surprises us.
Follow Evidence Where it Leads, Even When it Surprises Us
Dr. Joe Pesce is the National Science Foundation program officer for ALMA. Although he was referring to the debris disk study, he could have been referring to any of these planetary formation findings when he wrapped up the AAS session with the following thoughts.
“We are finding planets everywhere we look, and these fabulous results are showing us how planets form – both those around other stars and in our own Solar System. This research demonstrates how astronomy works and how progress is made, informing not only what we know about the field but also about ourselves.”
We always have more to learn if we dare to know.
Martian Meteorite Upsets Planet Formation Theory
Krypton in the Chassigny meteorite shows Mars accreted chondritic volatiles before nebular gases
Scientists on the Hunt for Planetary Formation Fossils Reveal Unexpected Eccentricities in Nearby Debris Disk
ALMA Images the Eccentric HD53143 Debris Disk
No signs (yet) of life on Venus
Proposed energy-metabolisms cannot explain the atmospheric chemistry of Venus
Astrobiology: 3 Questions We Need to Answer
Planet Formation Clarified by Young Star System
Planets Form from Stardust – Rapidly and Frequently