What Makes Something A Planet, According To An Astrophysicist?
“A dolphin may look like a fish, but it’s really a mammal. Similarly, the composition of an object is not the only factor in classifying it: its evolutionary history is inextricably related to its properties. Scientists will likely continue to argue over how to best classify all of these worlds, but it’s not just astronomers and planetary scientists who have a stake in this. In the quest to make organizational sense of the Universe, we have to confront it with the full suite of our knowledge.
Although many will disagree, moons, asteroids, Kuiper belt and Oort cloud objects are fascinating objects just as worthy of study as modern-day planets are. They may even be better candidates for life than many of the true planets are. But each object’s properties are inextricably related to the entirety of its formation history. When we try to classify the full suite of what we’re finding, we must not be misled by appearances alone.”
You’ve heard about the IAU’s definition, where in order to be a planet, you must pull yourself into hydrostatic equilibrium, orbit the Sun and nothing else, and gravitationally clear your orbit. You’ve also heard about the controversial new definition from geophysical/planetary science arguments, that planets should be based on their ability to pull themselves into a spheroidal shape alone.
Well, what about a third way: defining planets (and a whole classification scheme) based on astrophysical concerns alone? It’s time to start thinking about it!
Our Generation Is Not Getting A Moonshot, And This Is The Reason Why
“We could take equally bold steps today if we wanted to. There are literally thousands upon thousands of astronomers, physicists, engineers, technicians, computer scientists, hardware designers, rocket builders, habitat designers, and many other skilled professionals who would love to participate in a moonshot for a new generation: a generation that grew up where crewed spaceflight beyond low-Earth orbit was only a historical memory.
Instead of investing a substantial amount of resources in truly reaching towards new frontiers, we’re delegating them to uncrewed, robotic space probes. Sure, the amount of scientific information we can get out of them is much higher for a much lower cost, but getting the most bang-for-our-buck isn’t why we push the frontiers of knowledge. Instead, we’re taking baby steps where great strides are called for.”
Have you ever dreamed of traveling to another world? Even if you yourself aren’t game for the journey, have you dreamed of humanity achieving that goal? For most of us alive today, we have never lived during a time where human beings were present anyplace beyond low-Earth orbit. Unless something dramatically changes, that will likely remain true for the remainder of the century. Humans aren’t headed to the Moon, to Mars, to a satellite world in the outer Solar System, or to an interstellar destination unless we seriously take the initiative to re-invest in basic research and development. Until we start stably allocating resources, personnel, and R&D priorities towards these ends, we’re going to remain stuck here on Earth.
Read this if you want to get motivated towards changing the course of human civilization for the better.
Sorry, Black Holes Aren’t Actually Black
“If you have an astrophysical object that emits radiation, that immediately defies the definition of black: where something is a perfect absorber while itself emitting zero radiation. If you’re emitting anything, you aren’t black, after all.
So it goes for black holes. The most perfectly black object in all the Universe isn’t truly black. Rather, it emits a combination of all the radiation from all the objects that ever fell into it (which will asymptote to, but never reach, zero) along with the ultra-low-temperature but always-present Hawking radiation.
You might have thought that black holes truly are black, but they aren’t. Along with the ideas that black holes suck everything into them and black holes will someday consume the Universe, they’re the three biggest myths about black holes. Now that you know, you’ll never get fooled again!”
So, you thought you knew all there way to know about black holes? That if you get enough mass together in a small enough volume of space, you create an event horizon: a region from within which nothing can escape, not even light. So how is it, then, that black holes wind up emitting radiation, even long after the last particle of matter to fall into them has ceased?
There are two ways this occurs, and both are completely unavoidable. Black holes aren’t actually black, and this is how we know it.
This Is Everything That’s Wrong With Our Definition Of ‘Planet’
“There are many people who would love to see Pluto regain its planetary status, and there’s a part of me that grew up with planetary Pluto that’s extraordinarily sympathetic to that perspective. But including Pluto as a planet necessarily results in a Solar System with far more than nine planets. Pluto is only the 8th largest non-planet in our Solar System, and is clearly a larger-than-average but otherwise typical member of the Kuiper belt. It will never be the 9th planet again.
But that’s not necessarily a bad thing. We may be headed towards a world where astronomers and planetary scientists work with very different definitions of what attains planethood, but we all study the same objects in the same Universe. Whatever we call objects — however we choose to classify them — makes them no less interesting or worthy of study. The cosmos simply exists as it is. It’s up to the very human endeavor of science to make sense of it all.”
Next month will mark 13 years since the International Astronomical Union (IAU) officially defined the term planet and ‘Plutoed’ our Solar System’s (up-until-that-point) 9th planet. With an additional 13 years of knowledge, understanding, data, and discoveries, though, did they get the decision right?
Certainly, there were aspects that needed to be revised, but the IAU’s definition comes along with some major gaps and mistakes. We can do better! Come learn how.
No, Black Holes Will Never Consume The Universe
“Yes, there will be a very, very small number of stars, planets, asteroids and more that do get consumed by black holes, but it will be less than 0.1% of all the matter presently in the Universe. Even dark matter will remain in the outskirts of galaxies, unable to be eaten by black holes.
You might think that after googols and googols of years, anything still present in a galaxy will eventually be consumed, but don’t forget about Hawking radiation: eventually, all the Universe’s black holes will decay, too. Before any substantial fraction of the remaining galactic matter — normal or dark — can be devoured, every black hole in the Universe will have completely decayed away. If something dear to you does fall into a black hole, don’t despair. Try waiting instead. If you’re clever enough, you’ll not only get its energy back again someday, but most likely its information, too.”
About a month ago, I gave a talk in Hungary at their big international event: Brain Bar, where I spoke about the biggest myths about black holes. One of them is the idea that eventually, if you wait around for long enough, black holes will consume the entire Universe. It makes sense to think that this could happen, since gravity is real, there are close to a billion black holes in our galaxy, objects do randomly collide with one another, and gravitational radiation cause all bound masses to eventually inspiral into one another. But, as it turns out, something else happens first.
The overwhelming majority of matter will never find its way into a black hole, and black holes won’t consume the Universe. Here’s what happens instead.
7 Fascinating Facts About 2019’s Only Total Solar Eclipse
“3.) Optimally situated viewers will experience 4 minutes and 33 seconds of totality.
With Earth near aphelion and the Moon near perigee, it’s nearly twice the duration of 2017’s eclipse.”
On July 2, 2019, the world will experience a total solar eclipse: the only one of the year. Unlike the famous 2017 solar eclipse which spanned the continental United States, this year’s total solar eclipse occurs almost exactly coincident with both lunar perigee, where the Moon is closest to Earth, and solar aphelion, where the Sun is at its farthest point from Earth. July 2nd is just 2 days before our annual aphelion and 3 days before our monthly perigee, meaning that we’ll get 4 minutes and 33 seconds of totality during maximum eclipse: nearly twice as long as 2017′s maximum totality and the longest total solar eclipse we’ll experience until 2027.
What will we learn? What will we see? And how can you observe it from anywhere in the world? Find out these and more amazing facts before the eclipse passes!
Meet The Largest X-Ray Jet In The Universe
“Like all known active galaxies, Pictor A is powered by a supermassive black hole many millions to billions of times our Sun’s mass. Black holes can accelerate and eject infalling matter, leading to intense emissions. The light released spans the spectrum from high-energy X-rays to low-energy radio waves. The radio lobes of gas provide a medium for high-energy X-rays to interact with. When these interactions cause electrons to exceed the speed of sound in the gaseous medium, it creates intense shock waves.”
When you have an active galaxy, you can be pretty certain that there’s a supermassive black hole feeding on some matter nearby. If you’ve been paying attention, you’ll know that black holes don’t just devour matter, but that most of the matter that encounters them gets accelerated and ejected instead. This create large lobes of radio-emitting gas around many such galaxies, and in this one in particular, Pictor A, that provides exactly the right environment to create a spectacular feature. X-ray emissions, with energies many times that required to ionize atoms and molecules, slam into that matter, causing it to create free electrons that exceed the speed of sound in that medium. The result is that we get shock waves, and an overall X-ray jet that’s some 300,000 light-years long.
That makes this galaxy the one with the largest known X-ray jet in the Universe so far! Come get the full story, and many more beautiful images, here!
Ask Ethan: When Is The Earliest Sunrise And Latest Sunset Of The Year?
“We all know the solstices are the longest/shortest days off the year, but given the analemma, when are the earliest/latest sunrise/sunset times? Is it consistent at all latitudes?”
If the Earth’s axis were perfectly aligned with our orbital plane around the Sun, and if our orbit were perfectly circular instead of elliptical, the Sun would trace out the same path in the sky every single day. There would be no solstices or equinoxes; every day would be the same.
But we do rotate on a substantial tilt: 23.5 degrees. And our planet orbits in an ellipse, which means we move faster in our orbit when we’re closer to the Sun (near perihelion) than when we’re farther from the Sun (near aphelion). This means that not only does the Sun move throughout the year, and not only do days get shorter and longer, but sunset/sunrise times shift, too.
Funny story: your earliest sunrise/sunset is entirely dependent on your latitude, and almost certainly won’t occur on the longest day of the year. Find out why.
Ten Solstice Facts That Everyone Should Know
“9.) The solstices are neither the hottest nor coldest days of the year. This one is actually very specific to Earth: the hottest times of the year typically correspond to approximately 6 weeks after the summer solstice, and approximately 6 weeks after the winter solstice. Other planets don’t have this same phenomenon for one very important reason: they don’t have the majority of their surfaces covered in liquid water.
The oceans themselves, being composed of large quantities of water and containing approximately 1,000 times the mass of Earth’s atmospheres, contain a tremendous amount of heat, and are slow to change their temperatures. We might receive more (or less) energy from the Sun on the summer (or winter) solstices, but the oceans require time to heat up or cool down. Global average temperature extremes, therefore, usually occur in early August and February, rather than at the June and December solstices.”
The solstice, Latin for the Sun standing still in the sky, occurs whenever the Earth’s axial tilt reaches a maximum relative to the Earth’s orbital plane around the Sun. With a tilt of 23.5 degrees, but a tilt that’s independent of our elliptical orbit around the Sun, many surprising and counterintuitive facts arise.
Want to know as many of them as possible? Come get this remarkable and fascinating list of educational facts on this year’s solstice: June 21, 2019!
This Is Why Every Galaxy Doesn’t Have The Same Amount Of Dark Matter
“It isn’t the properties of one or two galaxies that will be the ultimate test of dark matter, however. Whether these galaxies are generic dwarf galaxies or our first examples of dark matter-free galaxies isn’t the point; the point is that there are hundreds of billions of these dwarf galaxies out there that are presently below the limits of what’s observable, detectable, or having their properties measured. When we get there, especially in the distant Universe and in post-interaction environments, we can fully expect to truly find this yet-unconfirmed population of galaxies.
If dark matter is real, it must be separable from normal matter, and that works both ways. We’ve already found the dark matter-rich galaxies out there, as well as isolated intergalactic plasma. But dark matter-free galaxies? They might be right around the corner, and this is why everybody is so excited!”
When the Universe was first born, everything was uniform. There was dark matter and normal matter everywhere, in the same 5-to-1 ratio in all structures. But then the Universe had to go and get messy. It formed stars and galaxies of different masses and sizes, and that’s where the trouble started. In large, massive galaxies, even cataclysms like supernovae or active supermassive black holes don’t eject very much normal matter. But in small galaxies, significant amounts of normal matter can get ejected, upping that ratio to dozens or event hundreds to one. That ejected matter doesn’t just go away, but can itself, at least in theory, form dark matter-free galaxies. Where are we in our understanding of galaxies, dark matter, and gravitation?
It’s just a small piece of the puzzle, but this explains why not every galaxy has the same 5-to-1 ratio you might naively expect!