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)
Ask Ethan: What Could Solve The Cosmic Controversy Over The Expanding Universe?
“As you pointed out in several of your columns, the cosmic [distance] ladder and the study of CMBR gives incompatible values for the Hubble constant. What are the best explanations cosmologists have come with to reconcile them?”
If you had two independent ways to measure a property of the Universe, you’d really hope they agreed with one another. Well, the situation we have with the expanding Universe is extremely puzzling: we have about 10 ways to do it, and the answers all fall into two independent and mutually incompatible categories. Either you make the measurement of an early, relic signal that’s observable today, and you get a value of 67 km/s/Mpc, with an uncertainty of about 1%, or you measure a distant object whose emitted light comes directly to our eyes through the expanding Universe, and you get a value of 73 km/s/Mpc, with an uncertainty of about 2%. It’s looking increasingly unlikely that any one group is wrong, in which case, we absolutely require some new, exotic physics to explain it.
While many ideas abound, there are five of them that are eminently testable in the next decade or so. Here’s how we could solve the expanding Universe controversy in the best way possible: with more and better science!
We Have Now Reached The Limits Of The Hubble Space Telescope
“Finally, there are the wavelength limits as well. Stars emits a wide variety of light, from the ultraviolet through the optical and into the infrared. It’s no coincidence that this is what Hubble was designed for: to look for light that’s of the same variety and wavelengths that we know stars emit.
But this, too, is fundamentally limiting. You see, as light travels through the Universe, the fabric of space itself is expanding. This causes the light, even if it’s emitted with intrinsically short wavelengths, to have its wavelength stretched by the expansion of space. By the time it arrives at our eyes, it’s redshifted by a particular factor that’s determined by the expansion rate of the Universe and the object’s distance from us.
Hubble’s wavelength range sets a fundamental limit to how far back we can see: to when the Universe is around 400 million years old, but no earlier.”
The Hubble Space Telescope, currently entering its 30th year of service, has literally revolutionized our view of the Universe. It’s shown us our faintest and most distant stars, galaxies, and galaxy clusters of all. But as far back as it’s taken us, and as spectacular as what it’s revealed, there is much, much more Universe out there, and Hubble is at its limit.
Here’s how far we’ve come, with a look to how much farther we could yet go. It’s up to us to build the tools to take us there.
This Is What Our Sun’s Death Will Look Like, With Pictures From NASA’s Hubble
“Single stars often shed their outer layers spherically, like 20% of planetary nebulae. Stars with binary companions frequently produce spirals or other asymmetrical configurations. But the most common shape for planetary nebulae is a bipolar morphology, containing two opposing jets. The leading explanation is that many stars rotate rapidly, which generates large-scale magnetic fields. Those fields accelerate the loosely-held particles populating the outer stellar regions along the dying star’s poles.”
Our Sun is in for a long life, having over 5 billion additional years until it becomes a red giant, and then will burn helium in its core until it’s approximately 7 billion years from now. But when its core exhausts its fuel, the tenuously-held outer layers will get expelled, while the core contracts down to a white dwarf. The intense heat and radiation from this phase will ionize the outer regions and illuminate the skies in a spectacular show known as a planetary nebula. Although this phase might last a mere 10,000 years, the death throes of Sun-like stars can be seen all throughout the galaxy, and is one of the most spectacular sights there is.
What will our Sun look like, and what do the Sun-like stars we see today, going through this phase, show and teach us? Take a look inside and find out!
Ask Ethan: Can We Find Exoplanets With Exomoons Like Ours?
“But, by far, the best possibility we have today is through direct measurement of a transiting exomoon. If the planet that’s orbiting the star can make a viable transiting signal, then all it will take is the same serendipitous alignment to have its moon transit the star, and sufficiently good data to tease that signal out of the noise.
This is not a pipe dream, but something that has already occurred once. Based on data taken by NASA’s Kepler mission, the stellar system Kepler-1625 is of particular interest, with a transiting light curve that not only displayed the definitive evidence of a massive planet orbiting it, but of a planet that wasn’t transiting with the exact same frequency you’d expect orbit after orbit.”
If you want to find an exoplanet, the most successful methods are to look for the effect it has on the light from it’s parent star. But what about if you wanted to find an exomoon? There are some subtle effects at play, but if we think hard about what they might be, we can come up with a series of methods that could reveal an exomoon’s presence indirectly, and pinpoint exactly where and when we could look to try and detect one directly. Thought to be a great technique for the upcoming James Webb Space Telescope to take advantage of TESS data, we’ve actually succeeded once already, using the Hubble/Kepler combo!
You may have missed it, but we think we’ve found the first exomoon as of late last year. What does the future hold for exomoons? Find out on this week’s Ask Ethan!
These Are The Top 10 Hubble Images Of 2018
“Year after year since its 1990 launch, Hubble keeps revolutionizing our view of the Universe. No other observatory continues to teach us so much. 28 years on, it’s still yielding uniquely spectacular scientific sights.”
There were a slew of scientific, astronomical breakthroughs made this past year, and Hubble was at the forefront of a great many of them. There was a tremendous dust storm enveloping Mars, and Hubble was there to capture it. Saturn’s rings are evaporating so quickly that they’ll be gone in 100 million years, and Hubble captured them. Ultraviolet light is created in great abundance in the nearby Universe from star-forming galaxies, and Hubble completed a survey of them. Ultra-distant galaxies form stars too, and Hubble was there to image them and measure how far it truly is to them. Galaxies speed through clusters; clusters contain stars ripped out of galaxies; nebulae race to form stars before the gas gets blown away by the existing ones. Through it all, Hubble was there.
What do the top 10 images of 2018 look like, and what do they teach us about the Universe? It’s a year-end list to remember, along with a feast for your eyes!
Scientists Can’t Agree On The Expanding Universe
“The question of how quickly the Universe is expanding is one that has troubled astronomers and astrophysicists since we first expansion was occurring at all. It’s an incredible achievement that multiple, independent methods yield answers that are consistent to within 10%, but they don’t agree with each other, and that’s troubling.
If there’s an error in parallax, Cepheids, or supernovae, the expansion rate may truly be on the low end: 67 km/s/Mpc. If so, the Universe will fall into line when we identify our mistake. But if the Cosmic Microwave Background group is mistaken, and the expansion rate is closer to 73 km/s/Mpc, it foretells a crisis in modern cosmology. The Universe cannot have the dark matter density and initial fluctuations 73 km/s/Mpc would imply.
Either one team has made an unidentified mistake, or our conception of the Universe needs a revolution. I’m betting on the former.”
The Universe is expanding: the observations overwhelmingly support that. It’s consistent with Einstein’s General Relativity; it work with the framework of the Big Bang; it allows us to quantify and predict the ultimate fate of our Universe.
But how fast, then, is the Universe expanding?
Scientists can’t agree, because there are three different techniques you can use to measure it. Two agree; one doesn’t.
So what gives? This is the controversy driving astrophysicists nuts at the moment. Come learn what it’s all about, along with my hunch as to what the resolution will be!
Who Really Discovered The Expanding Universe?
“Recently, what was known for generations as “Hubble’s Law” has now been renamed the Hubble-Lemaître law. But the point shouldn’t be to give credit to individuals who’ve been dead for generations, but rather for everyone to understand how we know the rules that govern the Universe, and what they are. I, for one, would be just as happy to drop all the names from all the physical laws out there, and simply to refer to them as what they are: the redshift-distance relation. It wasn’t the work of just one or two people that led to this breakthrough in discovering the expanding Universe, but of all the scientists I named here and many others as well. At the end of the day, it’s our fundamental knowledge of how the Universe works that matters, and that’s the ultimate legacy of scientific research. Everything else is just a testament to the all-too-human foible of vainly grasping at glory.”
In science, we have a tendency to name theories, laws, equations, or discoveries after the individual who made the greatest contribution towards its development. For generations, we credited Edwin Hubble for discovering the expanding Universe, as his contributions in the 1920s were absolutely tremendous. However, history has not only revealed that Georges
discovered the very law we had named after Hubble two years prior, but that many other people made essential contributions to that realization. The expanding Universe didn’t come about solely because of Hubble’s discoveries, and perhaps we can do better than crediting just a single person.
Here are a slew of advances that led to and supported the expanding Universe, showing that history and science relies on contributions far richer than that of a lone, genius scientist.
This Is How We Know There Are Two Trillion Galaxies In The Universe
“Over time, galaxies merged together and grew, but small, faint galaxies still remain today. Even in our own Local Group, we’re still discovering galaxies that contain mere thousands of stars, and the number of galaxies we know of have increased to more than 70. The faintest, smallest, most distant galaxies of all are continuing to go undiscovered, but we know they must be there. For the first time, we can scientifically estimate how many galaxies are out there in the Universe.
The next step in the great cosmic puzzle is to find and characterize as many of them as possible, and understand how the Universe grew up. Led by the James Webb Space Telescope and the next generation of ground-based observatories, including LSST, GMT, and the ELT, we’re poised to reveal the hitherto unseen Universe as never before.”
How many galaxies are there in the Universe? If you had asked Carl Sagan a generation ago, the answer might have been something vague, like billions and billions. Just a decade or two ago, people would have guesstimated around 100 billion, as deep surveys from Hubble could give us a count of galaxies both near-and-far in a small region of the sky. But those estimates aren’t necessarily any good, except to serve as lower limits. In order to understand how many galaxies must truly be out there, it requires us to understand both what the Universe is made of and what constitutes a galaxy. Only in the last few years have we reached that level of sophistication, and come up with what we believe, for the first time, is an accurate number.
That number? Two trillion. There are two trillion galaxies in the Universe. This is the story of how we know.
This Is How Hubble Will Use Its Remaining Gyroscopes To Maneuver In Space
“It might seem to be just another example of crumbling infrastructure in the United States, but you must neither underestimate Hubble nor the resourcefulness of astronomers and scientists and engineers overall. The two (or maybe three) remaining gyroscopes are of a new and upgraded design, designed to last five times as long as the original gyroscopes, which includes the one that recently failed. The James Webb Space Telescope, despite being billed as Hubble’s successor, is actually quite different, and will launch in 2021.
Even with one gyroscope, the Hubble Space Telescope should still be operational and capable of providing complementary observations to James Webb. This reduced-gyro mode has been planned for a long time. The only disappointment is that we may need to enter it so soon.”
One of the hallmarks of a successful NASA project is overengineering. Things will go wrong, break down, and degrade over time. One of the best examples is the Opportunity rover, which was designed for a 90 day mission and wound up living for nearly 15 years. But many people don’t appreciate how successfully overengineered Hubble is. Now well into its 28th year, it’s some 9 years removed from its final servicing mission. The gyroscopes that were installed included three of the old type and three of the new type, and the final old-style gyroscope has just failed.
Yet Hubble can continue operating and doing astronomy on just one gyroscope. Its demise has been greatly exaggerated; come learn the truth about Hubble today!