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The different types of planets barreling through space – ZME Science

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Planets come in all sha… planets come in various sizes. But, some of the most striking characteristics that set them apart are their physical and chemical particularities, which we use to categorize the myriad of planets we’ve found in space.

Image via JPL-Caltech.

I like planets. I like them so much I live on one. They’re heavy enough for gravity to make them round, their orbits are clear of debris, and they don’t burn like stars do. But, there’s a lot of variation in what they are and the experience they offer.

So, today, I’d thought it would be exciting to look at all the different types of planets — some of which we’ve seen in the great expanse of space, some of which we’re only expecting to find. In no particular order, they are:

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Brown Dwarfs

Artist’s impression of a T-type brown dwarf named 2MASSJ22282889-431026. The Hubble and Spitzer space telescopes observed the object to learn more about its turbulent atmosphere.
Image credits NASA / JPL-Caltech.

A star is a delicate system where gravity compresses and heats everything up while the nuclear fusion at their core pushes outwards. With too much pressure, electrons can’t move freely, so the reaction stops. With too much ‘boom’, there’s not enough pressure to keep the reaction going.

Teetering on the edge of starhood, brown dwarfs have outgrown any definition of a ‘planet’. Yet, they’re just not quite a star. Ranging from 13 to 80 times the mass of Jupiter, brown dwarfs are immense embers barreling through space, fusing deuterium and lithium to keep themselves slightly alight. However, they need yet more matter to be able to fight their own gravity, so they can’t ignite.

Brown dwarfs aren’t planets. They don’t form like planets — they form like stars. Instead of material slowly clumping together, brown dwarfs are born from clouds of gas collapsing in on themselves.

Gas Giants

Jupiter as snapped by the Juno probe.
Image credits NASA / JPL-Caltech.

The chonk de la chonk, gas giants are the largest planets to ever dot the universe. They are composed primarily (>90%) of hydrogen and helium (the two simplest elements in the periodic table) with traces of other compounds thrown in for good measure. Hydrogen and helium give these planets an overall brown-yellow-ocher palette, with water and ammonia clouds peppering their highest layers white. Owing to the nature of their bodies, these giants are blanketed by wild storms and furious winds.

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We don’t know much about their cores, only that it has to be immensely hot (around 20,000 Kelvin, K) and pressurized in there. The main hypotheses hold that gas giants either have molten rocky cores surrounded by roiling oceans of gas, diamond cores, or ones made of super-pressured (metallic) hydrogen nuggets.

Jupiter as snapped by the Juno probe.
Image credits NASA / JPL-Caltech.

They are sometimes called ‘failed stars’ because those two gases are what keeps stars running, but gas giants don’t have enough mass to spark nuclear fusion. We have two of them in the solar system, Jupiter and Saturn.

Most exoplanets we’ve found so far are gas giants — just because they’re huge and easier to spot.

Ice Giants

Picture of Neptune taken in August 1989, assembled using filtered images taken by Voyager 2.
Image credits NASA / JPL-Caltech / Kevin M. Gill.

Very similar to gas giants but won’t return your texts. Ice giants are believed to swap out hydrogen and helium (under 10% by weight) in favor of oxygen, carbon, nitrogen, and sulfur, which are heavier. Boiled down, we don’t really know what elements these planets are made of — their (admittedly thin) hydrogen envelopes hide the interior of the planets, so we can’t just go look. This outer layer is believed to closely resemble the nature of gas giants.

Still, it is believed that, while not entirely made of the ice we know and love here on Earth exactly, there is water and water ice in their make-up. They get their name from the fact that most of their constituent matter was solid as the planets were forming, and because planetary scientists refer to elements with freezing points above about 100 K (such as water, ammonia, or methane) as “ices”.

COROT-7c, an exoplanet located approximately 489 light years away in the constellation Monoceros. Seen here in an artistic simulation as a hot mini-Neptune.
Image credits MarioProtIV / Wikimedia.

Ice giants are, as per their name, quite gigantic, but they tend to be smaller than gas giants. However, owing to their much-denser make-up, they are also more massive overall. There are two ice giants in our solar system, Uranus and Neptune. Water, in the form of a supercritical ocean beneath their clouds, is believed to account for roughly two-thirds of their total mass.

Both ice giants and gas giants have primary atmospheres. The gas they’re made from was accreted (captured) as the planets were forming.

Rocky Planet

Artistic rendering of Mars based on topographic data.
Image in Public Domain.

Also known as terrestrial or telluric planets (from the Latin word for Earth), they are formed primarily of rock and metal. Their main feature is that they have a solid surface. Mercury, Venus, Earth, and Mars, the first four from the Sun, are the rocky planets of our solar system.

To the best of our knowledge rocky planets are formed around a metallic core, although the hypothesis of coreless planets has been floated around.

Atmospheres, if they have one, are secondary — formed from captured comets or created via volcanic or biological activity. Rocky planets also form primary atmospheres but fail to retain them. Secondary atmospheres are much thinner and more pleasant than those of Saturn or Uranus. That’s not to say a secondary atmosphere can’t influence its planet: Venus’s rampant climate disaster is a great example.

Composite image of Mercury’s north pole.
Image credits NASA.

Mercury, with a metallic core of 60–70% of its planetary mass, is as close as we’ve found to an Iron planet. Both it and the much more bling Carbon planets thus remain hypothetical. Another exciting and cool-named hypothetical class of rocky planets are Chthonians, the rock or metal cores of gas giants stripped bare.

Rocky worlds can harbor liquid water, terrain features, and potentially tectonic activity. Tectonically-active planets can also generate a magnetic field.

Comparison of best-fit size of the exoplanet Kepler-10c (middle) with Earth and Neptune.
Image via Wikimedia.

Such planets come in many different sizes. Earth is Earth-sized, Mercury is only about one third of it, while Kepler-10c is 2.35 times as large as our planet. Density is also a factor. Without going to a planet and studying its interior structure, it’s impossible to accurately estimate its density. As a rule of thumb, however, uncompressed density estimates for a rocky planet tend to be lower the farther away it orbits its star. It’s likely that planets closer to the star would thus have a higher metal (denser) content, while those further away would have higher silicate (lighter) content. Gliese 876 d is 7 to 9 times the mass of Earth.

The first extrasolar rocky planets were discovered in the early 1990s. Ironically, they were found orbiting a pulsar (PSR B1257+12), one of the most violent environments possible for a planet. Their estimated masses were 0.02, 4.3, and 3.9 times that of Earth’s.

Ocean planets

Ganymede, the largest and most massive moon in the Solar System, and its ninth largest body.
Its also an ocean moon.
Image via Wikimedia.

Planets that contain a large amount of water, either on the surface or subsurface. They’re an offshoot of the rocky planet, either covered in liquid water or an ice layer over liquid water. We don’t know very much about them or how many there are out there because we can’t yet spot liquid surface water, so we use atmosphere spectrometry as a proxy.

Earth is the only planet on which we’ve confirmed the existence of liquid water at the surface so far. And although water does cover around 71% of the Earth, it only makes up for 0.05% of its mass, so we’re not an Ocean planet. On these latter ones, waters are expected to run so deep that they would turn to (warm) ice even at high temperatures (due to the pressure).

This type of planet remains one of the likeliest to harbor extraterrestrial life.

Dwarf planets

True color image of Pluto taken by the  New Horizons craft.
Image via Wikimedia.

Fan-favorite Pluto, along with Ceres, Haumea, Makemake, and Eris are the dwarf planets of our solar system. Dwarf planets kind of stride the line between planets and natural satellites. They’re large enough to hold their own stable shape, even to hold moons themselves, but not enough to clear their orbit of other material.

Moons

Titan seen in visible light (center) and infrared (exterior).
Image credits NASA / JPL-Caltech / University of Nantes / University of Arizona.

Not technically planets because they orbit another planet, moons are nevertheless telluric bodies that vary in size from ‘large asteroid’ to ”larger than Mercury’. Titan, Saturn’s largest moon, has its own atmosphere.

There are six planets in the Solar System that sum up to 185 known natural satellites, while Pluto, Haumea, Makemake, and Eris also harbor their own moons.

Rogue planets

These are the planets your parents warned you about.

Rogue planets deserve a mention on this list despite the fact that they don’t orbit a star. They are, for all intents and purposes, planets that orbit the galactic core after being ejected from the planetary system in which they formed. It is also possible that, somehow, they formed free of any stellar host. PSO J318.5−22 is one such planet.

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SpaceX's Next Starship Prototype Taking Shape (Photos) – Space.com

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SpaceX’s next Starship prototype won’t be just a concept vehicle for much longer.

Construction of the test craft is proceeding apace, as two new photos posted on Twitter today (Sept. 17) by company founder and CEO Elon Musk reveal. 

One of the images shows the vehicle — apparently Starship Mk1, which is being assembled at SpaceX’s South Texas facility, near the village of Boca Chica — in the background, standing behind a building that contains a variety of parts and other equipment. (SpaceX is also building a similar prototype, called Starship Mk2, at the company’s Florida facilities, reasoning that a little intracompany competition will improve the vehicle’s final design.)

Related: SpaceX’s Starship and Super Heavy Mars Rocket in Pictures

“Droid Junkyard, Tatooine,” Musk said via Twitter, referring to Luke Skywalker’s home planet in the “Star Wars” movies. 

The other photo is a close-up view of a ring-shaped section being lowered onto the Mk1’s body. The billionaire entrepreneur had a joky caption for this one as well: “Area 51 of Area 51.”

The Mk1 and Mk2 follow in the footsteps of SpaceX’s Starhopper vehicle, which was retired after acing a big test flight last month. But the new vehicles are far more ambitious and more capable. Whereas Starhopper sported just a single Raptor engine and stayed within a few hundred feet of the ground, for example, the Mk1 and Mk2 will be powered by at least three Raptors and will go much higher.

SpaceX is aiming for a test flight that gets 12 miles (20 kilometers) up in October, followed by an orbital attempt “shortly thereafter,” Musk said late last month.

All of these steps are leading toward the final Starship, SpaceX’s planned Mars-colonizing craft. That Starship will be capable of carrying 100 passengers and will launch atop a huge rocket called the Super Heavy. Both of the elements, rocket and spaceship, will be fully and rapidly reusable, Musk has said.

The final Starship, as currently envisioned, will sport six Raptors, while the Super Heavy will be powered by 35 of the engines. Those numbers could change, however; Musk is scheduled to give a Starship design update on Sept. 28 from the South Texas site.

The Mk1 should be fully assembled by that time, he has said.

The Mk1 and Mk2 test campaigns won’t be terribly lengthy, if SpaceX’s planned schedules hold. Company representatives have said that the first operational flights of Starship, which are likely to be commercial satellite launches, could come as early as 2021. (Eventually, SpaceX plans to use Starship for all the company’s spaceflight needs, from interplanetary colonization missions to satellite launches to point-to-point trips around Earth.)

And SpaceX is targeting 2023 for a crewed mission of the vehicle: a flight around the moon booked by Japanese billionaire Yusaku Maezawa.

Mike Wall’s book about the search for alien life, “Out There” (Grand Central Publishing, 2018; illustrated by Karl Tate), is out now. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook

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Could We Intercept Interstellar Comet C/2019 Q4 Borisov? – Universe Today

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When ‘Oumuamua passed through our Solar System two years ago, it set off a flurry of excitement in the astronomical community. Here was the first-ever interstellar object that be observed by human trackers, and the mysteries surrounding its true nature and composition led to some pretty interesting theories. There were even some proposals for a rapid mission that would be able to rendezvous with it.

And now that a second interstellar object – C/2019 Q4 (Borisov) – has been detected traveling through the Solar System, similar proposals are being made. One of them comes from a group of scientists from the Initiative for Interstellar Studies (i4is) in the UK. In a recent study, they assess the technical feasibility of sending a mission to this interstellar comet using existing technology, and found that there were a few options!

In many ways, C/2019 Q4 (Borisov) represents an opportunity to conduct the kinds of research that were not possible with ‘Oumuamua. When that mystery object was first observed, it had already made its closest pass to the Sun, past Earth, and was on its way out of the Solar System. Nevertheless, what we were able to learn about ‘Oumuamua led to the conclusion that it was an entirely new class of celestial object.

Artist’s impression of the first interstellar asteroid/comet, “Oumuamua”. This unique object was discovered on Oct. 19th, 2017, by the Pan-STARRS 1 telescope in Hawaii. Credit: ESO/M. Kornmesser

In addition to those who ventured that it was either a comet or an asteroid, there were also those who theorized that ‘Oumuamua could be a fragment from a comet that exploded when passing close to our Sun, or even an extra-terrestrial solar sail. Another interesting find was the fact that similar objects likely pass through our Solar System on a regular basis (many of which stay).

For these reasons, a mission that could study such objects up close is very desirable. As Dr. Andreas M. Hein – the executive director of i4is’s board of directors, the chairman of its Technical Research Committee, and one of the co-authors on the recent study – told Universe Today via email:

“Investigating interstellar objects from a close distance would provide us with unique data about other star systems without actually flying to them. They might provide unique insights into the evolution and composition of other star systems and exoplanets in them. Interstellar objects are cool as it’s a bit like: If you can’t go to the mountain, let the mountain come to you. It will likely take many decades until we can send a spacecraft to another star. Hence, interstellar objects might be an intermediate solution for finding out more about other stars and their planets.”

What’s more, he claims, these objects have probably been travelling between star system for hundreds of thousands (or even millions) of years. As a result, they undoubtedly picked up material along the way or bear the marks of encounters with other objects or forces. In short, their composition and surface features can tell us a great deal about what is out there in the interstellar medium.

Artist’s illustration of a light-sail powered by lasers generated on the surface of a planet. Credit: M. Weiss/CfA

This is not the first time that i4is has proposed sending a spacecraft to rendezvous with an interstellar object. In 2017, Dr. Hein and several colleagues from i4is (who also co-authored this study) produced a paper titled “Project Lyra: Sending a Spacecraft to 1I/’Oumuamua (former A/2017 U1), the Interstellar Asteroid“, which was conducted with the help of the asteroid-prospecting company Asteroid Initiatives LLC.

The project was so-named because of ‘Oumuamua’s origins, which astronomers concluded came from the general direction of Vega – the brightest star in the northern constellation of Lyra. After taking into account the speed with which ‘Oumuamua was leaving the Solar System at the time – 26 km/s (93,600 km/h; 58,160 mph) – they determined that any proposal would be a trade-off between three factors.

These included when a mission could launch, the velocity it could achieve, and the time it would take to rendezvous with the object. Under the circumstances, they felt that the best option was to wait for future technological breakthroughs – such as those being pursued by Breakthrough Starshot (a concept for a laser-driven interstellar solar sail).

These conclusions have proven very applicable, thanks to the detection of a second interstellar object passing through our Solar System in as many years. In their most recent study, the research team once again used Optimum Interplanetary Trajectory Software (OITS) – which was developed by team-member Adam Hibberd – to assess all available options for sending a spacecraft to rendezvous with an interstellar object.

The Falcon Heavy's first flight. Each time the Heavy lifts off, it uses roughly 440 tons of fuel. Image: SpaceX
The Falcon Heavy’s first flight. Each time the Heavy lifts off, it uses roughly 440 tons of fuel. Image: SpaceX

These included the optimal launch vehicle (like NASA’s Space Launch System (SLS) or SpaceX’s Falcon Heavy) the optimal trajectory for the mission, and the best type of spacecraft. In the end, they determined that humanity has the capability of rendezvousing with an interstellar object using existing technology and came up with a mission architecture that could make that happen.

This mission would rely on a heavy-launch vehicle and could alternately employ a 2 ton (1.8 metric ton) or a 3 kg (6.6 lbs) CubeSat spacecraft. Depending on when it launched and what its preferred trajectory would be, it might also need to conduct a Jupiter flyby and Solar Oberth maneuver to catch up with C/2019 Q4 (Borisov). As Dr. Hein explained:

“Our results show that for both, ‘Oumuamua and C/2019 Q4 (Borisov), we already have the technology to visit these objects. Regarding ‘Oumuamua, we can launch a spacecraft towards it even beyond the year 2030. There is plenty of time to develop such a spacecraft. The case for C/2019 Q4 (Borisov) is a bit more tricky, as it is faster than ‘Oumuamua. But even for this object, we could have sent a two-ton spacecraft to it with a Falcon Heavy, if we would have launched it in 2018.”

“Later missions are also possible, but require a bigger launcher. Future telescopes will be able to detect such objects much earlier and with adequate preparation, we can send a spacecraft on an encounter mission. So we have the technology to do this and with the discovery of C/2019 Q4 (Borisov), we also know that we probably have plenty of opportunities to fly to such an object.”

Artist’s impression of the interstellar object, `Oumuamua, experiencing outgassing as it leaves our Solar System. Credit: ESA/Hubble, NASA, ESO, M. Kornmesser

Once again, the presence of an interstellar object in our Solar System is a major source of excitement. In addition to all the opportunities to learn from them, C/2019 Q4 and ‘Oumuamua are encouraging because of the implication their presence has. Not only do they confirm that objects from distant stars pass through our System pretty regularly; they also show that we are at a point where we can detect, track and study them.

But knowing that in the future, we will be able to study them up close is especially exciting! In fact, the ESA is currently working on a mission that could very be the one to rendezvous with a future interstellar object. It’s known as the Comet Interceptor, a “fast-class” concept consisting of three spacecraft that will wait in space until a pristine comet appears, rapidly catch up with it!

“We imagine two types of research,” Dr. Hein said. “First, remote-sensing, for example with a telescope taking pictures. Second, we can analyze material from the object directly by shooting an impactor into it and catching some of the particles from the dust plume which is generated with the main spacecraft. This would provide unique insights into the composition of the object.”

As for what this research could reveal, Dr. Hein has some thoughts on that too: “I can only speculate but we might see evidence that organic molecules, the building blocks for life, actually travel between star systems and who knows, maybe life itself might actually spread between stars in our galaxy.”

Further Reading: arXiv

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Physicists at MIT Shave Estimate of Mass of Neutrino “Ghost Particle” in Half – SciTechDaily

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KATRIN’s spectrometer, shown here, precisely measures the energy of electrons emitted in the decay of tritium, which has helped scientists come closer to pinning down the mass of the ghost-like neutrino. Credit: The KATRIN Collaboration

Joseph Formaggio explains the discovery that the ghostly particle must be no more than 1 electronvolt, half as massive as previously thought.

An international team of scientists, including researchers at MIT, has come closer to pinning down the mass of the elusive neutrino. These ghost-like particles permeate the universe and yet are thought to be nearly massless, streaming by the millions through our bodies while leaving barely any physical trace.

The researchers have determined that the mass of the neutrino should be no more than 1 electron volt. Scientists previously estimated the upper limit of the neutrino’s mass to be around 2 electron volts, so this new estimate shaves down the neutrino’s mass range by more than half.

The new estimate was determined based on data taken by KATRIN, the Karlsruhe Tritium Neutrino Experiment, at the Karlsruhe Institute of Technology in Germany, and reported at the 2019 Conference on Astroparticle and Underground Physics last week. The experiment triggers tritium gas to decay, which in turn releases neutrinos, along with electrons. While the neutrinos are quick to dissipate, KATRIN’s sequence of magnets directs tritium’s electrons into the heart of the experiment — a giant 200-ton spectrometer, where the electrons’ mass and energy can be measured, and from there, researchers can calculate the mass of the corresponding neutrinos.

Joseph Formaggio, professor of physics at MIT, is a leading member of the KATRIN experimental group, and spoke with MIT News about the new estimate and the road ahead in the neutrino search.

Q: The neutrino, based on KATRIN’s findings, can’t be more massive than 1 electron volt. Put this context for us: How light is this, and how big a deal is it that the neutrino’s maximum mass could be half of what people previously thought?

A: Well, that’s somewhat of a difficult question, since people (myself included) don’t really have an intuitive sense of what the mass is of any particle, but let’s try. Consider something very small, like a virus. Each virus is made up of roughly 10 million protons. Each proton weighs about 2,000 times more than each electron inside that virus. And what our results showed is that the neutrino has a mass less than 1/ 500,000 of a single electron!

Let me put it another way. In each cubic centimeter of space around you, there are about 300 neutrinos zipping through. These are remnants of the early universe, just after the Big Bang. If you added up all the neutrinos residing inside the sun, you’d get about a kilogram or less. So, yeah, it’s small.

Q: What went into determining this new mass limit for the neutrino, and what was MIT’s role in the search?

A: This new mass limit comes from studying the radioactive decay of tritium, an isotope of hydrogen. When tritium decays, it produces a helium-3 ion, an electron, and an antineutrino. We actually never see the antineutrino, however; the electron carries information about the neutrino’s mass. By studying the energy distribution of the electrons ejected at the highest energies allowed, we can deduce the mass of the neutrino, thanks to Einstein’s equation, E=mc2.

However, studying those high-energy electrons is very difficult. For one thing, all the information about the neutrino is embedded in a tiny fraction of the spectrum — less than 1 billionth of decays are of use for this measurement. So, we need a lot of tritium inventory. We also need to measure the energy of those electrons very, very precisely. This is why the KATRIN experiment is so tricky to build. Our very first measurement presented today is the culmination of almost two decades of hard work and planning.

MIT joined the KATRIN experiment when I came to Boston in 2005. Our group helped develop the simulation tools to understand the response of our detector to high precision. More recently, we have been involved in developing tools to analyze the data collected by the experiment.

Q: Why does the mass of a neutrino matter, and what will it take to zero in on its exact mass?

A: The fact that neutrinos have any mass at all was a surprise to many physicists. Our earlier models predicted that the neutrino should have exactly zero mass, an assumption dispelled by the discovery that neutrinos oscillate between different types. That means we do not really understand the mechanism responsible for neutrino masses, and it is likely to be very different than how other particles attain mass. Also, our universe is filled with primordial neutrinos from the Big Bang. Even a tiny mass has a significant impact on the structure and evolution of the universe because they are so aplenty.

This measurement represents just the beginning of KATRIN’s measurement. With just about one month of data, we were able to improve previous experimental limits by a factor of two. Over the next few years, these limits will steadily improve, hopefully resulting in a positive signal (rather than just a limit). There are also a number of other direct neutrino mass experiments on the horizon that are also competing to reach greater sensitivity, and with it, discovery!

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