Profile cover photo
Profile photo
Ethan Siegel
Science writer, professor and theoretical astrophysicist
Science writer, professor and theoretical astrophysicist

Ethan Siegel's interests
View all
Ethan Siegel's posts

Post has attachment
“5.) Venus. Venus is hell, literally. At a constant surface temperature of some 900 degrees Fahrenheit, no human-made lander has ever survived more than a couple of hours while touched down on our nearest neighboring planet. But the reason Venus is so hot is because of it’s thick, carbon-dioxide rich atmosphere laden with heat-trapping clouds of sulphuric acid. This renders the surface of Venus thoroughly inhospitable, but the surface isn’t the only place to look for life. In fact, speculation is rampant that perhaps something interesting is happening some 60 miles up! Above the cloud-tops of Venus, the environment is surprisingly Earth-like: similar temperatures, pressures, and less corrosive material. It’s conceivable that with its own unique chemical history, that environment is filled with carbon-based airborne life, something that a mission to Venus’ upper atmosphere could easily sniff out.”

The Earth, to the best of our knowledge, is the only inhabited world we have. The ingredients for life may be everywhere, from asteroids to nebulae to exoplanets and more, but so far, only Earth is confirmed to have life. While Earth-like planets around Sun-like stars at the right distance for liquid water on their surface might seem like the best place to look for life, we don’t necessarily need to go that far. Right here in our own cosmic backyard, our own solar system boasts eight potential candidates for worlds with life on them today. Some of them are planets, like Mars and Venus; others are moons, like Europa and Titan; even asteroids like Ceres or Kuiper belt objects like Pluto get in on the action. The life that might be present might not look like most of life on Earth, but unless we look at the likely locations of biological activity in situ, we simply won’t know for certain.

Come find out all eight possible locations, and see if you can come up with a better possibility than any of these!

Post has attachment
“In order to build the world of Westeros, we just need to scale it up. Instead of having a small asteroid-sized object orbiting a binary dwarf planet, we could have an Earth-sized world orbiting a twin gas giant. If you had, say, a Saturn-sized planet with a super-Earth orbiting it close by, or a massive gas giant orbited by the rocky core of Jupiter, any moons of those binary worlds — even Earth-sized moons — would have that same chaotic, tumbling behavior. Night and day will still be a reality on a world like this, as the Earth-sized moon would still rotate rapidly with respect to the Sun, but the rotational axis would be wildly unpredictable. This would cause large variations in both the onset of seasons and in the length of night/day, potentially even leading to months or years of darkness on end for part of the world.”

Imagine a world where you know that winter is coming, but you don’t know when, or for how long, or how severe it will be. Sounds like fiction, doesn’t it? In our own solar system, where planets orbit a single star in elliptical, well-separated orbits, this is extraordinarily unlikely. But if a binary giant planet existed in the habitable zone, and a world like Earth orbited both of them like an inner moon, it could give you exactly the effects you’re seeking. A large, massive double planet would exert irregular, differential gravitational forces on an external moon, causing it to tumble, rather than stably and consistently rotate on its axis. It could create large variations in seasons, which will be unpredictable in duration and onset. And it could, at least for parts of the world, plunge some of the regions into incredibly long, cold, dark winters.

If you think the night is dark and full of terrors now, wait until you see what it’s like on a world where you can’t even predict the seasons!

Post has attachment
“All five worlds are inclined at less than one degree to Pluto’s equator, indicating that there was no gravitational capture. While Pluto is reddish in color, the lack of volatiles is seen in all five moons, meaning that whatever impact likely created the moons also prevented these same moons from hanging onto the lightest elements and molecules. And finally, close-up studies of the four small moons — Styx, Nix, Kerberos, and Hydra — all indicate that these bodies coalesced out of multiple, smaller bodies that later became gravitationally bound.”

When the Hubble Space Telescope discovered additional moons of Pluto, beyond Charon, it was speculated that New Horizons might find more. After all, objects more than ten times as far away as Hydra, Pluto’s outermost moon, would still be in stable orbits. Yet, with five inner moons and nothing beyond, not even diffuse rings, the spacecraft came up empty. This isn’t a disappointment, though! Instead, New Horizons’ detailed observations of all five of Pluto’s moons point towards a tremendous picture: that the entire Plutonian system owes its origin to a massive, ancient collision. The debris kicked up created the five grey moons, in stark contrast to the reddish color of Pluto, in a near-perfect 1:3:4:5:6 resonance.

Where did Pluto’s moons come from? Come learn about the ‘Big Whack’ hypothesis, and how all we’ve learned about Pluto spectacularly confirms it!

Post has attachment
“The model goes through successive intervals of oscillating in two directions while expanding in the third, something like an elevator shaking left and right, back and forth, as it steadily ascends for a number of floors. But then, after a certain number of cycles, called an “era,” one of the oscillating directions swaps places with the expanding direction, and the model begins to grow along a different direction. In the elevator analogy, that would be as if an ascending elevator started to move to the right instead. That transition inaugurates another era, which lasts for a particular number of cycles before switching behavior again to a third direction. Oddly if one writes down the number of cycles for each era, the sequence seems as random as successful dice tosses.”

One of the more puzzling aspects of our Universe is that, no matter which direction we look in, no matter how far away we check, its properties appear to be practically identical. This is surprising, since no signal can reach from one disconnected region to another, and yet the Universe behaves as if everything began from the same initial state. We refer to this as the horizon problem. Before there was cosmic inflation, today’s leading solution to that problem (among others), there was the idea of a Mixmaster Universe, where a combination of oscillations and growth led to a Universe that got smoothed out by the dynamics of its evolution. Although it didn’t solve the horizon problem in details, the chaotic properties of a Mixmaster Universe provided physical and mathematical insights that are still useful today.

Paul Halpern has the historical and scientific facts on this fascinating topic, and simultaneously makes me glad I have a Kitchen Aid instead of a Sunbeam Mixmaster today!

Post has attachment
“5.) Skyward views of the Moon’s shadow.

The entire sky won’t become dark-as-night; only the portion within the Moon’s shifting shadow.”

If you’ve never seen a total solar eclipse before, you’ve likely heard about many of the features to look for, like the sky darkening during the day, the Sun disappearing, and the solar corona and, occasionally, stars becoming visible during the day. But if you take an enhanced view, either with binoculars, a telescope, or photography, so much more becomes apparent. The Sun’s corona extends for millions of kilometers in all directions, while plasma loops and the Moon’s surface are illuminated. The Moon’s shadow can be seen across portions of the daytime sky, and it’s not just stars but also planets that can become visible. And finally, if clouds appear in the upper atmosphere with just the right conditions, the end of totality might herald the fascinating optical phenomenon of iridescence.

Thanks to the extraordinary eclipse photography of Miloslav Druckmuller, you can get a preview of it all! Catch it on today’s Mostly Mute Monday.

"What about actual physics? If you have the full quantum state of a macroscopic system encoded, and particles like electrons, protons, nuclei, etc., are identical to and indistinguishable from one another, does it matter which particles are used? The “you” of today has no atoms in common with the “you” of 10 years ago, yet it’s still identifiable as you… isn’t it? The “you” a minute after you become a corpse (someday) and the “you” the minute before have virtually the same composition, yet one has the “you-ness” of the living you and the other doesn’t. So what is it that defines who you are? What you are?"

Now that quantum teleportation has been demonstrated between Earth and space, could transporters be up next? If you fall into a black hole, is there any way to prevent the atoms that make you up from falling apart? If the Universe didn't have deuterium, could you still, someday, have habitable planets like Earth? These questions and many more came up thanks to our commenters, and bring us our weekly dose of bonus science for Starts With A Bang.

Come check them all out on our comments of the week!

Post has attachment
“I’ve read some about this, more on just trying to live on Mars, which seems hard enough (and now we know the ‘soil’ there is toxic and kills bacteria rapidly). But terraforming as a reality for Mars? Seems the biggest problem is lack of a magnetic field so any atmosphere you make will get stripped away. […] why don’t we terraform Earth instead - it would be much easier!!”

Is terraforming a real possibility for Mars? It seems like one of the most inhospitable places we could have asked for: cold, small, barren, devoid of liquid water, with only a thin atmosphere, and with soil that’s toxic to terrestrial lifeforms. Yet Mars was once a wet, thriving planet, teeming with all the potential for life that an early Earth once possessed. Could it get there again? It’s certainly a more daunting task than any environmental crisis we can envision taking place on Earth, since we’d pretty much have to add an enormous amount of atmosphere to Mars to make it habitable. Even if we could, the atmosphere would be stripped away by the solar wind… but that might not be a dealbreaker!

If we could add that atmosphere, all those other problems would be pretty straightforward to deal with. Find out how on this edition of Ask Ethan!

Post has attachment
“The scientific story is not yet done, as there’s so much more of the Universe still to discover. Yet these 11 steps have taken us from a Universe of unknown age, no bigger than our own galaxy, made up mostly of stars, to an expanding, cooling Universe powered by dark matter, dark energy and our own normal matter, teeming with potentially habitable planets and that’s 13.8 billion years old, originating in a Big Bang which itself was set up by cosmic inflation. We know our Universe’s origin, it’s fate, what it looks like today, and how it came to be this way. May the next 100 years hold just as many scientific advances, revolutions, and surprises for us all.”

100 years ago, our conception of the Universe was so small it’s almost laughable. We still were mired in Newtonian thought, conceiving only of the stars within our own Milky Way, with a Universe that was perceived as static and unchanging, and where the stars which made it up perhaps even lived forever. Yet today, we have a Universe that’s expanding, cooling, full of dark matter and dark energy, and had a birthday 13.8 billion years ago: the Big Bang. More than that, we’ve been able to determine exactly how big the Universe is, where it came from, what happened before the Big Bang, and what its fate is today. We know how the elements were formed, how the stars live and die, what the Universe looks like on the largest scales, and how it got to be the way it is today.

How did this happen? One step of scientific investigation at a time! Here are the biggest jumps forward in each decade, going back 100 years.

Post has attachment
“If all you had were conventional hydrogen and helium, where hydrogen is made of one proton and helium is made of two protons and two neutrons, your proto-star would contract down rapidly, heating up to fusion temperatures in short order and emitting large amounts of high-intensity light. This radiation pushes against the nearby material that helped form the star in the first place, blowing it away from the star and overcoming gravity. You might form stars up to about three times the mass of the Sun, but the more massive ones — the ones we need to create an Earth-like world — would never come to exist.”

By time the first few minutes of the Big Bang are over, the Universe has formed all the elements it’s ever going to form until the first stars are born. At that point, the Universe is made out of 75% hydrogen and 25% helium, with only tiny, trace amounts of other isotopes and elements like deuterium, helium-3, and lithium-7. Yet if the Universe were truly hydrogen and helium only, you’d never be able to form a star more massive than about three times the Sun’s mass, preventing the creation of the heavy elements necessary for life! That tiny, trace amount of deuterium that the Big Bang creates, even though it’s just 0.0025% of the Universe, efficiently pushes back in the core of a young proto-star, delaying the amount of time it takes to ignite true fusion, and enabling stars to become tens or even hundreds of times as massive as our Sun. And yes, that’s more than enough for supernovae to occur.

Without this tiny inefficiency in the nuclear reactions taking place in the early Universe, the Earth and life on it could never have existed. Come get the scientific story of how this imperfection helped create you!

Post has attachment
"Just a few minutes after Monday's closest approach, Juno flew over the Great Red Spot, at an elevation of only 9,000 kilometers (5,600 miles). The three raw images that came back contain a huge amount of information within them. Taken in red, green, and blue filters, and then stacked together to make a composite, color image, these three images combined provide total coverage of the Great Red Spot."

On Monday, July 10th, the Juno spacecraft reached Perijove, or its closest approach to Jupiter, for the seventh time. Reaching a minimum elevation of only 3,500 km (2,200 miles), it found its images distorted into a compressed hourglass shape, due to its close proximity to the giant planet's upper atmosphere. Nevertheless, shortly after Perijove, it passed over the Great Red Spot, providing us with the closest images of this storm ever taken. And wow, were they not only spectacular, but after some detailed image processing, you can see different features teased out in there, including differentiation, eddies, and turbulence inside the spot.

We'll have to wait a while for the scientists to analyze the data from the other 8 instruments, but in the meantime, the first views are already here. Enjoy!
Wait while more posts are being loaded