Starts With A Bang Podcast #47 – Ice Giants At The Solar System’s Edge
What do we really know, and what mysteries are left to solve, about the outer worlds of our Solar System, and about the gas giant and ice giant worlds found throughout the Universe? Remarkably, if you had asked this same question 30 years ago, we would have had a quaint story about how planets form and why our Solar System has the planets it does, and we assumed that these rules would be extended to all solar systems in the galaxy and Universe. But with the deluge of exoplanet data, accompanied by better observations and simulations of our Solar System, that old story isn’t even the half of it.
I’m so lucky to get to interview Heidi Hammel for this edition of the podcast, who, as a bonus, was the lead investigator on the Hubble Space telescope when Comet Shoemaker-Levy 9 impacted Jupiter back in 1994! Come listen to one of my favorite interviews ever today!
(Image credit: NASA/Voyager 2)
Happy Birthday To Urbain Le Verrier, Who Discovered Neptune With Math Alone
“The other planets dutifully followed the laws of planetary motion, but Uranus appeared to violate them. Breaking Kepler’s laws, Uranus moved too quickly for decades, then at the right speed, then too slowly. The observations weren’t easily dismissable, but their physical cause was unknown. An additional planet beyond Uranus, gravitationally tugging on it, offered a potential solution. Determining the mass, orbital parameters, and location of an unseen world presented incredible calculational challenges.”
On March 11, 1811, Urbain Le Verrier was born. As a mathematician of tremendous skill in France, he had only a passing initial interest in astronomy, until the 1840s, when the influential François Arago suggested that he take up the puzzle of Uranus’ orbit, which appeared to violate the laws of planetary motion. Le Verrier theorized that if there were an outer planet beyond Uranus with the right mass and orbital parameters, it could cause these observed orbital anomalies. On August 31, 1846, Le Verrier composed a letter detailing his predictions and sent it to the Berlin Observatory. On September 23, the letter arrived. That very night, the portion of the sky where Le Verrier claimed a new planet should be was clear, and less than one degree away from his location, there it was: the planet Neptune.
Arago immortalized Le Verrier as the man who discovered a planet with the point of his pen. It remains an astronomical achievement of the highest order.
Triton, Not Pluto or Eris, Is The Kuiper Belt’s Largest World
“The result, today, is that the largest and most massive body ever to form in the Kuiper belt — 20% larger than Pluto; 29% more massive than Eris — is now Neptune’s largest moon: Triton. Today, Triton makes up 99.5% of the mass orbiting Neptune, an enormous departure from all the other giant planet systems we know of. The only explanation for its properties, especially its bizarre and unique orbit, is that Triton is a captured Kuiper belt object.
We often talk about icy moons with subsurface oceans as candidate worlds for life. We imagine large, distant, icy bodies as planets or dwarf planets in their own right. Triton was born not as a moon of Neptune, but as the largest and most massive Kuiper belt object to survive. You don’t cease to exist when you move locations, and neither did Triton. It’s the original king of the Kuiper belt, and its true origin story is a cosmic mystery that deserves to be solved.”
In October of 1846, just months after Neptune was discovered, a large moon was discovered around it: Triton. Today, Triton is a supremely unusual moon for a number of reasons, but the largest is that it rotates in the wrong direction. While Neptune orbits the Sun counterclockwise and spins counterclockwise on its tilted axis, Triton orbits in the opposite direction. The only way this could have happened is if it were a captured object. And that’s exactly what it looks like: a captured object from the Kuiper belt!
We know what it’s like and where it came from; the biggest mystery, now, is reconstructing how it came to be there. Come get the story on the true king of the Kuiper belt: Triton!
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Get Your Telescopes Ready: Neptune Is Coming
“Because of the periodic motions of the planets, Mars and Neptune had a close encounter just two years ago, but this year’s conjunction blows that one away in terms of proximity and viewing conditions. With a new Moon on December 7th, clear skies and the Geminid meteor shower growing towards its December 13th peak, it’s a great night to be outside for stargazing. Bring even a small telescope or a pair of binoculars with you, though, and the spectacular, blue sight of Neptune will be your reward.
For a few minutes of effort, you’ll see what no human prior to Galileo ever saw, except unlike Galileo, you won’t mistakenly record that you observed a fixed star. Instead, you’ll know you’re viewing the 8th and outermost planet in our Solar System, a planet that nobody knew existed a mere two centuries ago. This December 7th, we all have the opportunity to become astronomers. Make your chance count.”
On December 7th, 2018, a spectacular astronomical event will occur, but you won’t notice without binoculars or a telescope. Mars and Neptune will achieve an extremely close conjunction, separated by a mere 0.03 degrees at the moment of their closest approach. If you look at easily-identifiable Mars at that moment through binoculars or a telescope, you might see a faint, blue dot that appears to be a satellite companion of Mars. Only it’s not; it’s brilliant, blue Neptune, approximately 30 times as far away as our red neighbor! Galileo was the first to see Neptune, but he misidentified it for a fixed star. More than 200 years later, it remained undiscovered. But on December 7th, some 400 years later, you’ll have the opportunity of a lifetime that most humans will never get: the chance to see Neptune for yourself.
Next month, we’ll all have the chance to be astronomers, and to see a spectacular sight that generations of people never got. Make it count.
Ask Ethan: Can We Send A Cassini-Like Mission To Uranus Or Neptune?
“There is a window coming when spacecraft could be sent to Uranus or Neptune using Jupiter for a gravitational boost. What are the constraints on using this but being able to slow sufficiently for entering orbit around the “ice giants”?”
Going to the outer solar system is challenging. You have to launch with a tremendous speed, and then take advantage of planetary alignments and the gravity assist technique to bring you to an outer planet. If you want to go into orbit around a world out there, the challenge is even greater: you need to slow down and insert yourself into a stable, long-term orbit. That involves bringing fuel on board, and more fuel means more weight devoted to that, and less weight devoted to science instruments. In 2034, a spectacular opportunity will arise: a launch window that’s perfect for sending twin orbiters to Neptune and Uranus. The proposed ODINUS mission, a joint NASA/ESA venture, would teach us more about these outer worlds with hypothetical liquid oceans beneath their atmospheres than any other mission would. They may turn out to be as different as Earth and Venus are from one another.
We can send a Cassini-like mission to Uranus and Neptune, but there are some serious obstacles to overcome. Here’s how we just might do it!
In Science, And In Life, ‘Once A Failure’ Does Not Mean ‘Always A Failure’
“Adams initial failure to calculate and find Neptune did not prevent him from having later success with the Moon’s orbital motion. It in no way inhibited him in his greatest achievement: identifying the source of meteor showers, and confirming that Comet Tempel-Tuttle causes the Leonids. Similarly, Le Verrier’s immediate success in predicting the existence of Neptune didn’t lead to future success; his prediction of the existence of Vulcan, a proposed planet interior to Mercury to explain its orbit, failed to materialize.
In science, making a successful advance not only requires skill, talent, and persistence, but also a fair bit of luck. You can make mistakes along the way, in theory, in practice, and in judgment, but every new problem you tackle is a new chance to get it right. Treat your failures for what they are: momentary setbacks. In no way do they define your destiny.”
We all have our heroes, whether in sports, politics, war, art, music, or science. We like our heroes flawless: always right and victorious, never mistaken or beset by failure. But real life isn’t usually so clean. In fact, some of science’s greatest achievements were made by people who had colossal failures early in their careers. Perhaps no one exemplifies this more than John Couch Adams, who spectacularly failed to discover the planet Neptune in the mid-1840s, getting scooped by Urbain Le Verrier and his correspondents, led by the observers Galle and d’Arrest. Adams never blamed his corresponding observers, Airy and Challis, for their errors in judgment, and went on to solve one of astronomy’s greatest open problems: the origin of meteor showers.
Come get the incredible success-after-a-failure story of John Couch Adams, who should be known for much more than his failure to discover Neptune!