There’s a supermassive black hole in the center of our Milky Way galaxy. Could this black hole become a Quasar?
Previously, we answered the question, “What is a Quasar”. If you haven’t watched that one yet, you might want to pause this video and click here. … or you could bravely plow on ahead because you already know or because clicking is hard.
Should you fall in the latter category. I’m here to reward your laziness. A quasar is what you get when a supermassive black hole is actively feeding on material at the core of a galaxy. The region around the black hole gets really hot and blasts out radiation that we can see billions of light-years away.
Our Milky Way is a galaxy, it has a supermassive black hole at the core. Could this black hole feed on material and become a quasar? Quasars are actually very rare events in the life of a galaxy, and they seem to happen early on in a galaxy’s evolution, when it’s young and filled with gas.
Normally material in the galactic disk orbits well away from the the supermassive black hole, and it’s starved for material. The occasional gas cloud or stray star gets too close, is torn apart, and we see a brief flash as it’s consumed. But you don’t get a quasar when a black hole is snacking on stars. You need a tremendous amount of material to pile up, so it’s chokes on all the gas, dust, planets and stars. An accretion disk grows; a swirling maelstrom of material bigger than our Solar System that’s as hot as a star. This disk creates the bright quasar, not the black hole itself.
Quasars might only happen once in the lifetime of a galaxy. And if it does occur, it only lasts for a few million years, while the black hole works through all the backed up material, like water swirling around a drain. Once the black hole has finished its “stuff buffet”, the accretion disk disappears, and the light from the quasar shuts off.
Sounds scary. According to New York University research scientist Gabe Perez-Giz, even though a quasar might be emitting more than 100 trillion times as much energy as the Sun, we’re far enough away from the core of the Milky Way that we would receive very little of it – like, one hundredth of a percent of the intensity we get from the Sun.
This annotated artist’s conception illustrates our current understanding of the structure of the Milky Way galaxy. Image Credit: NASA
Since the Milky Way is already a middle aged galaxy, its quasaring days are probably long over. However, there’s an upcoming event that might cause it to flare up again. In about 4 billion years, Andromeda is going to cuddle with the Milky Way, disrupting the cores of both galaxies. During this colossal event, the supermassive black holes in our two galaxies will interact, messing with the orbits of stars, planets, gas and dust.
Some will be thrown out into space, while others will be torn apart and fed to the black holes. And if enough material piles up, maybe our Milky Way will become a quasar after all. Which as I just mentioned, will be totally harmless to us. The galactic collision? Well that’s another story.
It’s likely our Milky Way already was a quasar, billions of years ago. And it might become one again billions of years from now. And that’s interesting enough that I think we should stick around and watch it happen. How do you feel about the prospects for our Milky Way becoming a quasar? Are you a little nervous by an event that won’t happen for another 4 billion years?
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Brightest star Sirius (lower center) rules the anthropocene night. Credit and copyright: Alan Dyer.
What’s the brightest star you can see in the sky tonight?
If you live below 83 degrees north latitude, the brightest star in the sky is Canis Alpha Majoris, or Sirius. Seriously, (bad pun intended) the -1st magnitude star is usually the fifth brightest natural object in the sky, and sits high to the south on February evenings… but has it always ruled the night? Continue reading “What is the Brightest Star in the Sky, Past and Future?”
Artist's impression of the interior of Mars. Credit: NASA/JPL
For thousands of years, human beings have stared up at the sky and wondered about the Red Planet. Easily seen from Earth with the naked eye, ancient astronomers have charted its course across the heavens with regularity. By the 19th century, with the development of powerful enough telescopes, scientists began to observe the planet’s surface and speculate about the possibility of life existing there.
However, it was not until the Space Age that research began to truly shine light on the planet’s deeper mysteries. Thanks to numerous space probes, orbiters and robot rovers, scientists have learned much about the planet’s surface, its history, and the many similarities it has to Earth. Nowhere is this more apparent than in the composition of the planet itself.
Structure and Composition:
Like Earth, the interior of Mars has undergone a process known as differentiation. This is where a planet, due to its physical or chemical compositions, forms into layers, with denser materials concentrated at the center and less dense materials closer to the surface. In Mars’ case, this translates to a core that is between 1700 and 1850 km (1050 – 1150 mi) in radius and composed primarily of iron, nickel and sulfur.
This core is surrounded by a silicate mantle that clearly experienced tectonic and volcanic activity in the past, but which now appears to be dormant. Besides silicon and oxygen, the most abundant elements in the Martian crust are iron, magnesium, aluminum, calcium, and potassium. Oxidation of the iron dust is what gives the surface its reddish hue.
Composite image showing the size difference between Earth and Mars. Credit: NASA/Mars Exploration
Magnetism and Geological Activity:
Beyond this, the similarities between Earth and Mars’ internal composition ends. Here on Earth, the core is entirely fluid, made up of molten metal and is in constant motion. The rotation of Earth’s inner core spins in a direction different from the outer core and the interaction of the two is what gives Earth it’s magnetic field. This in turn protects the surface of our planet from harmful solar radiation.
The Martian core, by contrast, is largely solid and does not move. As a result, the planet lacks a magnetic field and is constantly bombarded by radiation. It is speculated that this is one of the reasons why the surface has become lifeless in recent eons, despite the evidence of liquid, flowing water at one time.
Despite there being no magnetic field at present, there is evidence that Mars had a magnetic field at one time. According to data obtained by the Mars Global Surveyor, parts of the planet’s crust have been magnetized in the past. It also found evidence that would suggest that this magnetic field underwent polar reversals.
This observed paleomagnetism of minerals found on the Martian surface has properties that are similar to magnetic fields detected on some of Earth’s ocean floors. These findings led to a re-examination of a theory that was originally proposed in 1999 which postulated that Mars experienced plate tectonic activity four billion years ago. This activity has since ceased to function, causing the planet’s magnetic field to fade away.
Map from the Mars Global Surveyor of the current magnetic fields on Mars. Credit: NASA/JPL
Much like the core, the mantle is also dormant, with no tectonic plate action to reshape the surface or assist in removing carbon from the atmosphere. The average thickness of the planet’s crust is about 50 km (31 mi), with a maximum thickness of 125 km (78 mi). By contrast, Earth’s crust averages 40 km (25 mi) and is only one third as thick as Mars’s, relative to the sizes of the two planets.
The crust is mainly basalt from the volcanic activity that occurred billions of years ago. Given the lightness of the dust and the high speed of the Martian winds, features on the surface can be obliterated in a relatively short time frame.
Formation and Evolution:
Much of Mars’ composition is attributed to its position relative to the Sun. Elements with comparatively low boiling points, such as chlorine, phosphorus, and sulphur, are much more common on Mars than Earth. Scientists believe that these elements were probably removed from areas closer to the Sun by the young star’s energetic solar wind.
After its formation, Mars, like all the planets in the Solar System, was subjected to the so-called “Late Heavy Bombardment.” About 60% of the surface of Mars shows a record of impacts from that era, whereas much of the remaining surface is probably underlain by immense impact basins caused by those events.
The North Polar Basin is the large blue low-lying area at the northern end of this topographical map of Mars. Credit: NASA/JPL/USGS
These craters are so well preserved because of the slow rate of erosion that happens on Mars. Hellas Planitia, also called the Hellas impact basin, is the largest crater on Mars. Its circumference is approximately 2,300 kilometers, and it is nine kilometers deep.
The largest impact event on Mars is believed to have occurred in the northern hemisphere. This area, known as the North Polar Basin, measures some 10,600 km by 8,500 km, or roughly four times larger than the Moon’s South Pole – Aitken basin, the largest impact crater yet discovered.
Though not yet confirmed to be an impact event, the current theory is that this basin was created when a Pluto-sized body collided with Mars about four billion years ago. This is thought to have been responsible for the Martian hemispheric dichotomy and created the smooth Borealis basin that now covers 40% of the planet.
Scientists are currently unclear on whether or not a huge impact may be responsible for the core and tectonic activity having become dormant. The InSight Lander, which is planned for 2018, is expected to shed some light on this and other mysteries – using a seismometer to better constrain the models of the interior.
Hellas Planitia extends across about 50° in longitude and more than 20° in latitude. From data from the Mars Orbiter LaserAltimeter (MOLA). Credit: NASA
Other theories claim that Mars lower mass and chemical composition caused it to cool more rapidly than Earth. This cooling process is therefore believed to be what arrested convection within the planet’s outer core, thus causing its magnetic field to disappear.
Mars also has discernible gullies and channels on its surface, and many scientists believe that liquid water used to flow through them. By comparing them to similar features on Earth, it is believed these were were at least partially formed by water erosion. Some of these channels are quite large, reaching 2,000 kilometers in length and 100 kilometers in width.
Yes, Mars is much like Earth in many respects. It’s a rocky planet, has a crust, mantle, and core, and is composed of roughly the same elements. As our exploration of the Red Planet continues, we are learning more and more about its history and evolution. Someday, we may find ourselves settling on that rock, and relying on its similarities to create a “backup location” for humanity.
If you’ve read your share of sci-fi, and I know you have, you’ve read stories about another Earth-sized planet orbiting on the other side of the Solar System, blocked by the Sun. Could it really be there?
No. Nooooo. No. Just no.
This is a delightful staple in science fiction. There’s a mysterious world that orbits the Sun exactly the same distance as Earth, but it’s directly across the Solar System from us; always hidden by the Sun. Little do we realize they know we’re here, and right now they’re marshalling their attack fleet to invade our planet. We need to invade counter-Earth before they attack us and steal our water, eat all our cheese or kidnap our beloved Nigella Lawson and Alton Brown to rule as their culinary queen and king of Other-Earth.
Well, could this happen? Could there be another planet in a stable orbit, hiding behind the Sun? The answer, as you probably suspect, is NO. No. Nooooo. Just no.
Well, that’s not completely true. If some powerful and mysterious flying spaghetti being magically created another planet and threw it into orbit, it would briefly be hidden from our view because of the Sun. But we don’t exist in a Solar System with just the Sun and the Earth. There are those other planets orbiting the Sun as well. As the Earth orbits the Sun, it’s subtly influenced by those other planets, speeding up or slowing down in its orbit.
So, while we’re being pulled a little forwards in our orbit by Jupiter, that other planet would be on the opposite side of the Sun. And so, we’d speed up a little and catch sight of it around the Sun. Over the years, these various motions would escalate, and that other planet would be seen more and more in the sky as we catch up to it in orbit.
Eventually, our orbits would intersect, and there’d be an encounter. If we were lucky, the planets would miss each other, and be kicked into new, safer, more stable orbits around the Sun. And if we were unlucky, they’d collide with each other, forming a new super-sized Earth, killing everything on both planets, obviously.
Diagram of the five Lagrange points associated with the sun-Earth system, showing DSCOVR orbiting the L-1 point. Image is not to scale. Credit: NASA/WMAP Science Team
What if there was originally two half-Earths and they collided and that’s how we got current Earth! Or 4 quarter Earths, each with their own population? And then BAM. One big Earth. Or maybe 64 64th Earths all transforming and converging to form VOLTREARTH.
Now, I’m now going to make things worse, and feed your imagination a little with some actual science. There are a few places where objects can share a stable orbit. These locations are known as Lagrange points, regions where the gravity of two objects create a stable location for a third object. The best of these are known as the L4 and L5 Lagrangian points. L4 is about 60-degrees ahead of a planet in its orbit, and L5 is about 60-degrees behind a planet in its orbit.
A small enough body, relative to the planet, could hang out in a stable location for billions of years. Jupiter has a collection of Trojan asteroids at its L4 and L5 points of its orbit, always holding at a stable distance from the planet. Which means, if you had a massive enough gas giant, you could have a less massive terrestrial world in a stable orbit 60-degrees away from the planet.
Grumpy Cat has the correct answer. Credit: grumpycat.com
Well, it was a pretty clever idea. Unfortunately, the forces of gravity conspire to make this hidden planet idea completely impossible. Most importantly, when someone tells you there’s a hidden planet on the other side of the Sun, just remember these words:
No.
Nooooo.
No.
Go ahead and name your favorite sci-fi stories that have used this trope. Tell us in the comments below.
Thanks for watching! Never miss an episode by clicking subscribe. Our Patreon community is the reason these shows happen. We’d like to thank Gary Golden and the rest of the members who support us in making great space and astronomy content. Members get advance access to episodes, extras, contests, and other shenanigans with Jay, myself and the rest of the team.
False color radar topographical map of Venus provided by Magellan. Credit: Magellan Team/JPL/NASA
Venus was once considered a twin to Earth, as it’s roughly the same size and is relatively close to our planet. But once astronomers looked at it seriously in the past half-century or so, a lot of contrasts emerged. The biggest one — Venus is actually a hothouse planet with a runaway greenhouse effect, making it inhospitable to life as we know it. Here are some more interesting facts about Venus.
1. Venus’ atmosphere killed spacecraft dead very quickly: You sure don’t want to hang around on Venus’ surface. The pressure there is so great that spacecraft need shielding to survive. The atmosphere is made up of carbon dioxide with bits of sulfuric acid, NASA says, which is deadly to humans. And if that’s not bad enough, the temperature at the surface is higher than 470 degrees Celsius (880 degrees Fahrenheit). The Soviet Venera probes that ventured to the surface decades ago didn’t last more than two hours.
2. But conditions are more temperate higher in the atmosphere: While you still couldn’t breathe the atmosphere high above Venus’ surface, at about 50 kilometers (31 miles) you’ll at least find the same pressure and atmosphere density as that of Earth. A very preliminary NASA study suggests that at some point, we could deploy airships for humans to explore Venus. And the backers suggest it may be more efficient to go to Venus than to Mars, with one large reason being that Venus is closer to Earth.
Artist’s conception of the High Altitude Venus Operational Concept (HAVOC) mission, a far-out concept being developed by NASA, approaching the planet. Credit: NASA Langley Research Center/YouTube (screenshot)
3. Venus is so bright it is sometimes mistaken for a UFO: The planet is completely socked in by cloud, which makes it extremely reflective to observers looking at the sky on Earth. Its brightness is between -3.8 and -4.8 magnitude, which makes it brighter than the stars in the sky. In fact, it’s so bright that you can see it go through phases in a telescope — and it can cast shadows! So that remarkable appearance can confuse people not familiar with Venus in the sky, leading to reports of airplanes or UFOs.
4. And those clouds mean you can’t see the surface: If you were to look at Venus with your eyes, you wouldn’t be able to see its surface. That’s because the clouds are so thick that they obscure what is below. NASA got around that problem when it sent the Magellan probe to Venus for exploration in the 1990s. The probe orbited the planet and got a complete surface picture using radar.
Artist’s impression of the surface of Venus Credit: ESA/AOES
5. Venus has volcanoes and a fresh face: Venus has fresh lava flows on its surface, which implies that volcanoes erupted anywhere from the past few hundred years to the past three million years. What this means is there are few impact craters on the surface, likely because the lava flowed over them and filled them in. While scientists believe the volcanoes are responsible, the larger question is how frequently this occurs.
6. Venus has a bizarre rotation: Venus not only rotates backwards compared to the other planets, but it rotates very slowly. In fact, a day on Venus (243 days) lasts longer than it takes the planet to orbit around the Sun (225 days). Even more strangely, the rotation appears to be slowing down; Venus is turning 6.5 minutes more slowly in 2014 than in the early 1990s. One theory for the change could be the planet’s weather; its thick atmosphere may grind against the surface and slow down the rotation.
Artist’s conception of Venus Express doing an aerobraking maneuver in the atmosphere in 2014. Credit: ESA–C. Carreau
7. Venus has no moons or rings: The two planets closest to the Sun have no rings or moons, which puts Venus in the company of only one other world: Mercury. Every other planet in the Solar System has one or the other, or in many cases both! Why this is is a mystery to scientists, but they are doing as much comparison of different planets as possible to understand what’s going on.
8. Venus appears to be a spot where spacecraft go to extremes: We briefly mentioned the Venera probes that landed on the surface, but that’s not the only unusual spacecraft activity at Venus. In 2014, the European Space Agency put an orbiter — that’s right, a spacecraft not designed to survive the atmosphere — into the upper parts of Venus’ dense atmosphere. Venus Express did indeed survive the encounter (before it ran out of gas), with the goal of providing more information about how the atmosphere looks at high altitudes. This could help with landings in the future.
As you can see, Venus is an interesting, mysterious, and extremely hostile world. With such a corrosive atmosphere, such incredible heat, a volcanically-scarred surface, and thick clouds of toxic gas, one would have to be crazy to want to live there. And yet, there are some who believe Venus could be terraformed for human use, or at the very least explored using airships, in the coming generations.
But that’s the thing about interesting places. Initially, they draw their fair share of research and attention. But eventually, the dreamers and adventurers come.
Look at the Moon. Have you ever noticed the Moon looks so big when it’s down on the horizon, but way smaller when it’s nearly overhead? What’s going on here? Turns out, you fell for the oldest trick in the book: the Moon Illusion.
Look at that Moon. It looks so big and full. Way bigger than it normally does. I wonder what’s going on to make it look so big? Maybe it’s closer and brighter? Maybe the atmosphere is distorting it like a lens? Or maybe, I’m just a human being, and I just fell for the oldest trick in the book: the Moon Illusion. Which really sounds more like a 80’s spy thriller novel than anything else. What I’m saying is, don’t believe your eyes.
The Moon is always the same size, and the distance varies by only a small amount during its orbit. As a result, the Moon is roughly the same size in the sky every night. Even though it looks huge on the horizon, it’s identical to when it’s directly overhead.
Don’t believe me? The Moon and your pinky fingernail when you hold your arm out at length, are about the same size. Next time the Moon’s in the sky, try it out, and you’ll see. Then try this out on one of those nights when the Moon just looks so big and fat. It’ll be it’s exactly the same size as it was before.
Look at this picture. Look at this collection of Moons, taken one after the other from Moonrise until the Moon is high in the sky. Exactly the same size! Every time! So what’s going on here?
The problem is up here, in my meat-thinky parts. For some reason, when the Moon is down on the horizon, we think it’s larger than when it’s directly overhead. But why? Bad news, we’re not actually sure yet. We’re still piling up the list of cognitive biases that make us think it’s a good idea to stay on an airplane that’s on fire or convince us to wait it out in our homes when there’s a tornado headed straight for us instead of evacuating like the nice people on the radio say.
How we perceive the moon’s size may have much to do with what’s around it. In this illustration, most of us seen the bottom moon as smaller, but they’re both exactly the same size. Crazy, isn’t it? Credit: NASA
One idea is that the Moon looks bigger on the horizon because it looks farther away. When we see stuff in the sky, like clouds, birds or airplanes, they seem tiny. But when we see the Moon, compared to closer objects on the horizon, like trees and buildings, our brain freaks out and decides that it’s actually larger.
Fun fact! It turns out our brain is really bad at knowing how big things actually are, and it’s easily tricked by the stuff around it. Here’s an optical illusion called the Ebbinghaus illusion. See those circles in the middle? They’re the same size in each example. But because of the other circles around them, our brain can’t deal. Normally buildings and trees are big. And yet they seem tiny compared to the Moon on the horizon.
I did say that it’s mostly the same distance, every night but the Moon actually does get bigger and smaller in the sky. It’s following an elliptical orbit around the Earth. At its closest point, the Moon gets about 363,000 km. And then at its furthest point, it’s about 405,000 km. So that is a bit of a difference, but seriously, you’d need a really good telescope to be able to tell, and it takes almost a month to make this journey from one end to the other.
Moon timelapse. Credit: Cory Schmitz
Trust me, you can’t tell. Or you know what, you can tell, you’re right. It’s just me, and everyone else, for us regular mortals, our brains are fooled. So next time your friend mentions how huge the Moon looks, feel free to explain the cold hard facts to them. Let them know that their brain is lying to them, and how they’re easily deceived. Then laugh and mock them for their amusing little human frailties. Then, I suppose you might be looking for new friends… but you will have enlightened them to the way of their wrongness, and that’s a gift that keeps on giving.
Well, did you fall for this? Did you think the Moon looks huge on the horizon, or are you somehow immune to the Moon illusion? If so, tell us your secret in the comments below.
Thanks for watching! Never miss an episode by clicking subscribe. Our Patreon community is the reason these shows happen. We’d like to thank Gerald Szesko and the rest of the members who support us in making great space and astronomy content. Members get advance access to episodes, extras, contests, and other shenanigans with Jay, myself and the rest of the team.Want to get in on the action? Click here.
Caloris in Color – An enhanced-color view of Mercury from the cameras on board the MESSENGER spacecraft. The circular, orange area near the center-top of the disc is Caloris Basin. Credit: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington
Close by the Sun is Mercury, a practically atmosphere-like world that has a lot of craters. Until NASA’s MESSENGER spacecraft arrived there in 2008, we knew very little about the planet — only part of it had been imaged! But now that the spacecraft has been circling the planet for a few years, we know a heck of a lot more. Here is some stuff about Mercury that’s useful to know.
1. Mercury has water ice and organics.
This may sound surprising given that the planet is so close to the Sun, but the ice is in permanently shadowed craters that don’t receive any sunlight. Organics, a building block for life, were also found on the planet’s surface. While Mercury doesn’t have enough atmosphere and is too hot for life as we know it, finding organics there demonstrates how those compounds were distributed throughout the solar system. There’s also quite a bit of sulfur on the surface, something that scientists are still trying to understand since no other planet in the Solar System has it in such high concentrations.
2. The water ice appears younger than we would expect.
Close examination of the ice shows sharp boundaries, which implies that it wasn’t deposited that long ago; if it was, the ice would be somewhat eroded and mixed in with Mercury’s regolith surface. So somehow, the ice perhaps came there recently — but how? What’s more, it appears the ice deposits on the Moon and the ice deposits on Mercury are different ages, which could imply different conditions for both of the bodies.
A forced perspective view of Mercury’s north pole (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
3. Mercury has an atmosphere that changes with its distance to the Sun.
The planet has a very thin atmosphere that is known as an “exosphere” (something that is also present on the Moon, for example.) Scientists have detected calcium, sodium and magnesium in it — all elements that appear to change in concentration as the planet gets closer and further from the Sun in its orbit. The changes appear to be linked to how much solar radiation pressure falls on the planet.
4. Mercury’s magnetic field is different at its poles.
Mercury is somehow generating a magnetic field in its interior, but it’s quite weak (just 1% that of Earth’s). That said, scientists have observed differences in the north and the south pole magnetic strength. Specifically, at the south pole, the magnetic field lines have a bigger “hole” for charged particles from the Sun to strike the planet. Those charged particles are believed to erode Mercury’s surface and also to contribute to its composition.
Illustration of MESSENGER in orbit around Mercury (NASA/JPL/APL)
5. Despite Mercury’s weak magnetic field, it behaves similarly to Earth’s.
Specifically, the magnetic field does deflect charged particles similarly to how Earth does, creating a “hot flow anomaly” that has been observed on other planets. Because particles flowing from the Sun don’t come uniformly, they can get turbulent when they encounter a planet’s magnetic field. When plasma from the turbulence gets trapped, the superheated gas also generates magnetic fields and creates the HFA.
6. Mercury’s eccentric orbit helped prove Einstein’s theory of relativity.
Mercury’s eccentric orbit relative to the other planets, and its close distance to the Sun, helped scientists confirm Einstein’s general theory of relativity. Simply put, the theory deals with how the light of a star changes when another planet or star orbits nearby. According to Encyclopedia Britannica, scientists confirmed the theory in part by reflecting radar signals off of Mercury. The theory says that the path of the signals will change slightly if the Sun was there, compared to if it was not. The path matched what general relativity predicted.
A hot flow anomaly, or HFA, has been identified around Mercury (Credit: NASA/Duberstein)
7. Mercury is hard to spot in the sky, but has been known for millennia.
Mercury tends to play peekaboo with the Sun, which makes it somewhat of an observing challenge. The planet rises or sets very close to when the Sun does, which means amateur astronomers are often fighting against twilight to observe the tiny planet. That being said, the ancients had darker skies than we did (no light pollution) and were able to see Mercury pretty well. So the planet has been known for thousands of years, and was linked to some of the gods in ancient cultures.
8. Mercury has no moons or rings.
Scientists are still trying to understand how the Solar System formed, and one of the ways they do so is by comparing the planets. Interesting to note about Mercury: it has no rings or moons, which makes it different from just about every other planet in our Solar System. The exception is Venus, which also has no moons or rings.
A full Moon flyby, as seen from Paris, France. Credit and copyright: Sebastien Lebrigand.
Shining like a beacon in Earth’s sky is the Moon. We’ve seen so much of it in our lifetimes that it’s easy to take it for granted; even the human landings on the Moon in the 1960s and 1970s were eventually taken for granted by the public.
Fortunately for science, we haven’t stopped looking at the Moon in the decades after Neil Armstrong took his first step. Here are a few things to consider about Earth’s closest big neighbor.
Artist's impression of New Horizons' encounter with Pluto and Charon. Credit: NASA/Thierry Lombry
As the New Horizons spacecraft gets closer and closer to Pluto in advance of its July 2015 flyby, it manages to and gathers more and more information. As a result, we learning more about the dwarf planet on an almost regular basis.
Pluto is now becoming more to the public than just the planet that no longer was; before long, we’ll be able to understand much about its atmosphere, its moons and how it fits into the story of the Solar System’s history. Here are some of the most interesting things we know about Pluto so far.
1. Its definition of “dwarf planet” is controversial: Back in 2006, the International Astronomical Union deemed Pluto is a dwarf planet and not a planet. The reasoning came after a few other objects were discovered far out in the Solar System that are close to Pluto’s size. That said, the principal investigator for New Horizons, Alan Stern, does not agree with the definition. At the time of the vote, he pointed out that the IAC’s definition of planet was not completely true of any larger body; for example, Earth does not clear the entire neighborhood of debris, which is one of the parts of the definition.
2. Pluto has several moons: For decades, astronomers knew of Pluto and its moon, Charon. The two are so close in size that some people considered the system a double planet, but now that’s thrown in doubt with the dwarf planet designation. In any case, in the last decade humanity has discovered several more moons as telescope resolution and observing techniques improved. The other moons are called Nix, Hydra, Kerberos and Styx. For now we don’t know much about these smaller moons because it’s so difficult to resolve features on their tiny size.
HST Image of Pluto-Charon system. Also shown are Nix and Hydra. Image Credit: NASA/ESA
3. Charon might have an ocean on it: It seems unbelieveable that Charon could have an ocean given it’s so far away from the Sun, but at least one study suggests that it could be possible. Essentially, the tidal force imparted by Pluto’s gravity early in Charon’s history could have stretched the moon’s insides and warmed them up enough to create liquid. That said, it’s also possible that the ocean is now frozen as Charon’s orbit is not as eccentric as it was in the past.
4. Charon’s formation could have spawned the other moons: As with our own Moon, some scientists believe Charon was created after a large object smashed into Pluto billions of years ago. This would have created a chain of debris circling the dwarf planet, which eventually coalesced into Charon. However, the other moons we know of near Pluto have almost exact resonances with Charon. This suggests that they also formed from the debris, one study says.
Footage of Charon, captured by NASA’s New Horizons spacecraft, taken in July 2014. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
5. Pluto has an atmosphere: Pluto is a tiny world, but like the Moon and Mercury it does have a very tenuous atmosphere that is called an “exosphere.” Astronomers first spotted signs of it in 1985. As Pluto passed in front of a star, they saw the star very slightly dim before Pluto completely blocked the star. The composition of this atmosphere is mostly made up of nitrogen and methane, and it freezes when Pluto is furthest from the Sun.
6. Pluto can get closer to the Sun than Neptune: We used to think of Pluto as the furthest planet from the Sun, but in reality its orbit is so eccentric that it comes closer to the Sun than Neptune. According to NASA, its average distance from the Sun is 39.5 astronomical units (Earth-Sun distances), but it can come as close as 29.7 AU and as far away as 49.7 AU. It was last “inside” Neptune’s orbit between 1979 and 1999.
Pluto’s surface as viewed from the Hubble Space Telescope in several pictures taken in 2002 and 2003. Though the telescope is a powerful tool, the dwarf planet is so small that it is difficult to resolve its surface. Astronomers noted a bright spot (180 degrees) with an unusual abundance of carbon monoxide frost. Credit: NASA
7. Astronomers think Pluto looks a lot like Neptune’s moon, Triton: Let’s be clear that Triton and Pluto have very different histories; for example, Triton was likely captured by Neptune long ago, an event that drastically altered its surface and its insides. But Pluto and Triton likely do have some similarities: the frozen volatiles (elements with low boiling points), the faint nitrogen atmospheres, and their similar composition of ice and rock. Scientists are pulling out old Voyager 2 pictures to make the comparisons as Pluto pictures arrive from New Horizons.
8. Pluto could have a ring system: It’s not a guarantee, but at least one research team suggests that debris floating around Pluto could coalesce into a faint ring system. This wouldn’t be a large surprise, by the by, as we already know of at least one asteroid that has rings — so it is possible. Researchers on New Horizons will also be on the lookout for more moons and interesting features on Pluto’s surface such as cracks.
Artist's conception of the solar system, often used in the Eyes on the Solar System 3D Simulator. Credit: NASA
While most of us are stuck on planet Earth, we’re lucky enough to have a fairly transparent atmosphere. This allows us to look up at the sky and observe changes. The ancients noticed planets wandering across the sky, and occasional visitors such as comets.
Thousands of years ago, most thought the stars ruled our destiny. Today, however, we can see science at work in the planets, asteroids and comets close to home. So why take a look at the Solar System? What can it teach us?
1. The definition of a planet and a moon is fuzzy.
We all know of that famous International Astronomical Union vote in 2006 where Pluto was demoted from planethood into a newly created class called “dwarf planets.” But the definition drew controversy among some, who pointed out that no planet — dwarf or otherwise — perfectly clears the neighborhood in its orbit of asteroids, for example. Moons are considered to orbit around planets, but that doesn’t cover situations such as moons orbiting asteroids or double planets, for example. Goes to show you the Solar System requires more study to figure this out.
2. Comets and asteroids are leftovers.
No, we don’t mean leftovers to eat — we mean leftovers of what the Solar System used to look like. So while it’s easy to get distracted by the weather and craters and prospects for life on planets and moons, it’s important to remember that we must also pay attention to the smaller bodies. Comets and asteroids, for example, could have brought organics and water ice to our own planet — providing what we need for life.
Four images of Comet 67P/Churyumov–Gerasimenko taken on Nov. 30, 2014 by the orbiting Rosetta spacecraft. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
3. The planets are all on the same “plane” and orbit in the same direction.
When considering the IAU’s definition of planets, we come up with eight: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. You’ll notice that these bodies tend to follow the same path in the sky (called the ecliptic) and that they orbit the Sun in the same direction. That supports the leading theory for the Solar System’s formation, which is that the planets and moons and Sun formed from a large gas and dust cloud that condensed and spun.
4. We’re nowhere near the center of the galaxy.
We can measure vast distances across the universe by looking at things such as “standard candles” — a type of exploding stars that tend to have the same luminosity, which makes it easier to predict how far away they are from us. At any rate, looking at our neighborhood, we’ve been able to figure out we’re nowhere near the Milky Way galaxy’s center. We’re about 165 quadrillion miles away from the center supermassive black hole, NASA says, which is probably a good thing.
A still photo from an animated flythrough of the universe using SDSS data. This image shows our Milky Way Galaxy. The galaxy shape is an artist’s conception, and each of the small white dots is one of the hundreds of thousands of stars as seen by the SDSS. Image credit: Dana Berry / SkyWorks Digital, Inc. and Jonathan Bird (Vanderbilt University)
5. But the Solar System is bigger than you think.
Beyond the orbit of Neptune (the furthermost planet), it takes a long time to leave the Solar System. In 2012, some 35 years after leaving Earth on a one-way trip to the outer solar Solar System, Voyager 1 passed through the area where the Sun’s magnetic and gas environment gives way to that of the stars, meaning that it is interstellar space. That was an astounding 11 billion miles (17 billion kilometers) away from Earth, or roughly 118 equivalent Earth-sun distances (astronomical units).
6. The Sun is hugely massive.
Just how massive? 99.86% of the Solar System’s mass is in our local star, which goes to show you where the real heavyweight is. The Sun is made up of hydrogen and helium, which shows you that these gases are far more abundant in our neighborhood (and the Universe generally) than the rocks and metals we are more familiar with here on Earth.
Solar prominences and filaments on the Sun on September 18, 2014, as seen with a hydrogen alpha filter. Credit and copyright: John Chumack/Galactic Images.
7. We haven’t finished searching for life here.
So we know for sure that life exists on Earth, but that doesn’t rule out a whole bunch of other places. Mars had water flowing on it in the ancient past, and has frozen water at its poles — making astrobiologists think it might be a good candidate. There also are a range of icy moons that could have oceans with life below the surfaces, such as Europa (at Jupiter) and Enceladus (at Saturn). There’s also the interesting world of Titan, which has “prebiotic chemistry” — chemistry that was a precursor to life — on its surface.
8. We can use the Solar System to better understand exoplanets.
Exoplanets are so far away, and so small in our telescopes, that it’s difficult to see very much detail in their atmospheres. But by looking at the chemistry of Jupiter, for example, we can make some predictions about gas giants further afield. If we look at Earth and Neptune, we can get a better sense of the range of planetary sizes on which life could exist (those “super-Earths” and “mini-Neptunes” you sometimes hear mentioned.) And even looking at where water freezes in our own Solar System can help us better understand the ice line in other locations.
We have written articles about the solar system for Universe Today. Here are facts about the planets in the Solar System. We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.
