Sciency Words: Ultra-Cool Dwarf Star

March 10, 2017March 5, 2017 ~ J.S. Pailly ~ 2 Comments

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Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us expand our scientific vocabularies together. Today’s term is:

ULTRA-COOL DWARF STAR

At some point, I want to profile each of the planets in the TRAPPIST-1 system one by one for my Exoplanet Explorer series. But it’s too early for that. Right now, we don’t know much about these planets except that they’re there.

But I can say something about TRAPPIST-1 itself. It’s a type of star called an ultra-cool dwarf star.

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Apparently TRAPPIST-1 has just barely enough mass to cause hydrogen fusion in its core. That means that for a star, it doesn’t produce a whole lot of energy, and thus its temperature is relatively low. Based on my rough math and statistics I got from Wikipedia, it looks like TRAPPIST-1 is less than half the temperature of our Sun.

This is one of the things that makes TRAPPIST-1 so interesting to me, and why it’s really starting to capture my imagination. It’s not just about all those Earth-like planets. The star itself helps set a lower limit for just how small and cold stars can be.

TRAPPIST-1: A Mini-Solar System

March 8, 2017March 5, 2017 ~ J.S. Pailly ~ 4 Comments

Right now, TRAPPIST-1 is getting a ton of attention. If feels like just about every single telescope on Earth or in Earth-orbit has been stealing glances of this very tiny star and its seven Earth-like planets.

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But we’ve discovered lots of other exoplanets, many of them Earth-like, and many of them in multi-planet systems. So why is TRAPPIST-1 getting so much special attention?

There Could Be Aliens!

Okay, yes. There could be aliens.

But I doubt it. TRAPPIST-1 is a flare star. We’ve met flare stars before. You don’t want to live near one.

Also, these planets are so close to their parent star that they are almost certainly tidally locked, with one side perpetually facing the sun and the other side perpetually turned away from it. Katy Perry could write a song about how hot and cold these planets must get.

Still, it’s not impossible for life to evolve under these conditions. Just don’t get your hopes up.

An Astrophysicist’s Dream Come True

There’s still a lot I haven’t read yet about TRAPPIST-1, and no doubt there’s even more information still to come. But at this point, I’m getting the impression that this miniaturized solar system is like an astrophysicist’s dream come true. Here’s why I think that:

From our vantage point here on Earth, these planets pass directly in front of their star (i.e.: they “transit” their sun). This is convenient for us. It’s a lot easier to collect data about transiting planets than non-transiting ones.
These planets are all very close to their parent star, and therefore they all have relatively short orbital periods. That means more transits and more opportunities to collect data.
There are so many planets so tightly packed together that it’s easy for us to study the gravitational interactions between them.
And again, because these planets have short orbital periods, these gravitational interactions are sort of accelerated compared to similar interactions in our own Solar System or in other star systems we’re currently observing. I imagine these interactions are also much stronger, since the planets are so much closer together.

TRAPPIST-1 is basically a mini-solar system running on fast-forward. We can collect loads of data about it in a matter of days or weeks, rather than years or decades, and use that data to refine our current theories about solar system dynamics.

That, I think, is the real reason TRAPPIST-1 and its seven planets are such a big deal. At least that’s what’s got me the most excited about them, and why I think we’ll be hearing a lot about the TRAPPIST-1 system for many years to come.

If we happen to discover alien life there as well, that’ll just be an added bonus.

Sciency Words: Earth Similarity Index

March 3, 2017March 3, 2017 ~ J.S. Pailly ~ 5 Comments

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EARTH SIMILARITY INDEX

As I’m sure you’ve heard by now, astronomers have discovered seven planets orbiting a nearby star called TRAPPIST-1. Even more exciting, most or all of these new worlds are being described as Earth-like planets. But what does that actually mean?

You’d be surprised by how many “Earth-like” planets/moons we have right here in our own Solar System.

Ag16 Earth-like Worlds — From left to right: Venus, Earth, Mars, and Titan (Saturn’s largest moon).

Earth-like is a rather vaguely defined term. So in 2011, a paper published in the journal Astrobiology attempted to establish an official mathematical system for calculating just how Earth-like an exoplanet is. It’s called the Earth Similarity Index or E.S.I.

Basically, the E.S.I. takes certain characteristics of a planet that can be quantified—such as a planet’s mass, radius, temperature, etc—and compares them to Earth’s. An E.S.I. score of zero indicates a planet that has absolutely nothing in common with Earth, while an E.S.I. of one means the planet is an exact match for Earth… at least with regard to the characteristics being measured and included in our calculations.

Of course even a planet with an E.S.I. of one is not necessarily habitable, so the same Astrobiology paper also proposes a Potential Habitability Index or P.H.I. But that, I think, is a Sciency Word for another day.

P.S.: If you want to dive into the math behind the E.S.I., click here.

Sciency Words: Light Curve

February 24, 2017February 20, 2017 ~ J.S. Pailly ~ 5 Comments

It’s been almost a week since I arrived at KIC 8462852, better known as Tabby’s Star, and discovered that the aliens really are building a megastructure. I still have a lot of questions, but the aliens aren’t giving me a lot of answers, and I think it’s time I moved on.

Which brings me to today’s edition of Sciency Words.

$Sciency Words MATH$

Each week, we take a closer look at some science or science-related term to help us all expand our scientific vocabularies together. Today’s term is:

LIGHT CURVE

We met astronomer Bradley Schaefer in Wednesday’s post. Writing for Scientific American, he defines a light curve as “a measure of brightness as a function of time.”

So the light curve of a star with a constant brightness would be a straight line. If you found small, symmetrical dips in that line, that might mean there’s a planet in orbit, especially if the dips appear at regular intervals. Here’s an example of what that looks like, courtesy of NASA.

Other patterns of dips or spikes along a light curve could tell you if you’re looking at a binary star, or a flare star, or a variable star… looking at light curves is a great way to study stars.

As for Tabby’s star, its light curve is apparently a straight line most of the time, aside from tiny fluctuations that typically indicate solar flares and/or sunspots. In other words, Tabby’s star looks normal.

And then abruptly, dips appear in the light curve. Asymmetrical dips, as opposed to the symmetrical dips caused by transiting planets. In some cases, the line doesn’t so much dip as plunge downward, and that means… umm… astronomers do not know what that means.

Any serious discussion about Tabby’s Star should really begin with its weird, almost spastic light curve. I’m choosing to end here, however, because the aliens have made it clear that I’m not welcome.

Now I need to find another megastructure to study, and the best way to do that is to examine the light curves of other stars.

More Megastructure Mystery

February 22, 2017February 20, 2017 ~ J.S. Pailly ~ 5 Comments

On Monday, I arrived at KIC 8462852, better known as Tabby’s Star, and discovered that yes, the aliens really are building a megastructure. My next question is: how long has this been going on?

These aliens are not turning out to be all that friendly. Fortunately, there’s been some investigative work done back on Earth.

Astrophotography has been around for well over a century now. Even though no one paid much attention to Tabby’s Star until recently, that region of the sky has been photographed before. So following the publication of Tabetha Boyajian’s WTF paper, astronomer Bradley Schaefer started checking those old photographic plates.

And according to Schaefer’s findings, Tabby’s Star has been decreasing in brightness since at least 1890. It would seem the megastructure has been growing in size, obscuring more and more of the star, for quite some time now.

But can we trust the accuracy of those old photographic plates? According to astronomer Michael Hippke and colleagues, no. No we can’t. The degree of uncertainty is too high, Hippke claims, to make a conclusive determination about Tabby’s Star’s brightness over time.

There’s been a pretty intense argument between Schaefer and Hippke ever since. If nothing else, it’s an excellent example of how scientists debate each other. Click here to read Schaefer’s side of it, and click here for Hippke’s.

So if Schaefer is right, construction of the megastructure may have been underway circa 614 C.E. (that’s 1890 C.E. minus the 1276 years it takes for light from Tabby’s Star to reach Earth). And if Hippke’s right… well, who knows when the aliens got started? They’re certainly not telling.

Tabby’s Megastructure Mystery

February 20, 2017February 20, 2017 ~ J.S. Pailly ~ 11 Comments

So I’ve flown my spaceship all the way out to KIC 8462852, better known as Tabby’s Star, and what do you know? The aliens really are building a megastructure out here.

This whole situation is pretty weird, I know; but the weirdest thing is that when I check my ship’s sensors, I can’t detect any thermal emissions from the megastructure or any of the spaceships involved in constructing it.

The lack of thermal emissions (or the lack of an “infrared excess,” as the experts call it) is one of the main reasons why Tabetha Boyajian and other legitimate scientists don’t really buy the alien megastructure hypothosis.

Think about it. If Tabby’s Star hosts an active work zone, with spaceships flying around and construction workers welding space girders and stuff, you’d expect all that activity to produce some heat. Even without the construction activity, the megastructure itself should be pretty warm due to the star it encircles.

And all that heat should be detectable in the form of infrared radiation. But whether you observe Tabby’s Star with a telescope back on Earth or the sensor grid of my imaginary spaceship, the total amount of infrared light is exactly what you’d expect from an F-type main-sequence star. No more, no less.

Since I’m here, I decided to ask one of the alien construction workers about this. Here’s what he told me: “Yeah, we been masking our thermal emissions. What of it? We don’ts wants nobody snooping in our business. Now scram, smelly human!”

Not exactly the answer I was expecting, but I guess I’ll take what I can get.

P.S.: If you want to learn more about Tabby’s Star and how citizen science helped uncover its mysterious behavior, I strongly recommend this SciShow interview with Tabetha Boyajian. That’s where I first learned about the “infrared excess” issue that I discussed in today’s post.

Sciency Words: Tabby’s Star

February 17, 2017February 16, 2017 ~ J.S. Pailly ~ 5 Comments

TABBY’S STAR

Something’s wrong with a star named KIC 8462852. It flickers. It dims by as much as 22% for no apparent reason. This is an F-type main-sequence star, meaning it’s only a little bit larger than our Sun. F-type stars shouldn’t behave like this.

KIC 8462852 is sometimes called the WTF Star, because of the paper that first described its abnormal fluctuations in brightness. That paper was subtitled “Where’s the Flux?”

The star is also known (and perhaps better known) as Tabby’s Star, in honor of Tabetha Boyajian, the lead author on that paper.

There are several possible explanations for what might be happening to Tabby’s Star, but it’s the least likely explanation that’s gotten the most hype. Could it be aliens? SETI decided to check it out. They didn’t find anything. But still… it could be aliens.

Massive alien starships might be transiting the star, blocking some of its light. Or perhaps there are enormous space stations orbiting the star. Or maybe we’ve caught an advanced alien civilization in the act of building some kind of megastructure (like a Dyson sphere) completely encircling their sun.

Most professional astronomers do not think it’s aliens. Tabetha Boyajian herself doesn’t seem to take the idea seriously and often jokes about the crazy emails she gets from people who do. And to be perfectly clear, I do not take this alien megastructure hypothesis seriously either.

But just to be sure, I’ve decided to hop into my imaginary spaceship and fly out to KIC 8462852, just so I can see for myself what’s really going on. Wish me luck! I’ll let you know what I find next week.

Planet Pailly: The Movie Trailer

February 9, 2017February 8, 2017 ~ J.S. Pailly ~ 4 Comments

Please read this in your best movie trailer voice:

* * *

In a world where science fiction writers often forget about science, one man wanted to do his research.

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And one muse told him he should totally do that.

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Coming February 15, 2017, these two will set out in their imaginary spaceship, continuing their voyages through the Solar System and beyond, and learning as much about science as their tiny brains can hold.

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Coming soon to an internet near you. This blog not yet rated by the MPAA.

Life on Mars: The Hunt for Martian Dinosaurs

December 28, 2016December 27, 2016 ~ J.S. Pailly ~ 5 Comments

Can Mars support life? Is there anything living on Mars right now? It sometimes seems like Mars is desperately trying to convince us that the answer to both questions is yes.

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If you’re hunting for alien life in the Solar System, there are four places you should pay attention to: Mars, Europa, Enceladus, and Titan. Now a thought recently occurred to me—a thought that I’m sure has occurred to other people before: in an astrobiological sense, these four worlds sort of represent the past, present, and future.

Mars: a place where alien life might have existed and thrived in the past.
Europa and Enceladus: places where life may exist and thrive in the present.
Titan: a place where life might start to evolve and thrive sometime in the future (assuming it hasn’t started already).

Regarding Mars, there was clearly a time when rivers, lakes, and oceans of liquid water covered the Martian surface. There’s growing evidence that at least some of the organic chemicals necessary for life were also present. Therefore it’s easy to imagine a time millions or perhaps billions of years ago when Mars had a biosphere as rich and robust as prehistoric Earth’s.

Obviously that robust biosphere is gone now. Even when we hear about the possibility that life still exists on present-day Mars, it’s generally assumed that this life would be only a remnant of what came before. The microbial survivors of whatever wiped out the Martian dinosaurs, so to speak.

Someday (hopefully soon), humans will travel to Mars. When we get there, we may find that all the Martians are long dead. That might seem a bit depressing, but actually I’m kind of excited by the idea that the fossilized remains of Martian dinosaurs might be there, waiting for us to come dig them up.

Sciency Words: Frost Line

December 23, 2016December 23, 2016 ~ J.S. Pailly ~ 10 Comments

Welcome to a very special holiday edition of Sciency Words! Today’s science or science-related term is:

FROST LINE

When a new star is forming, it’s typically surrounded by a swirling cloud of dust and gas called an accretion disk. Heat radiating from the baby star plus heat trapped in the disk itself vaporizes water and other volatile chemicals, which are then swept off into space by the solar wind.

But as you move farther away from the star, the temperature of the accretion disk tends to drop. Eventually, you reach a point where it’s cold enough for water to remain in its solid ice form. This is known as the frost line (or snow line, or ice line, or frost boundary).

Of course not all volatiles freeze or vaporize at the same temperature. When necessary, science writers will specify which frost line (or lines) they’re talking about. For example, a distinction might be made between the water frost line versus the nitrogen frost line versus the methane frost line, etc. But in general, if you see the term frost line by itself without any specifiers, I think you can safely assume it’s the water frost line.

Even though our Sun’s accretion disk is long gone, the frost line still loosely marks the boundary between the warmth of the inner Solar System and the coldness of the outer Solar System. The line is smack-dab in the middle of the asteroid belt, and it’s been observed that main belt asteroids tend to be rockier or icier depending on which side of the line they’re on.

It was easier for giant planets like Jupiter and Saturn to form beyond the frost line, since they had so much more solid matter to work with. And icy objects like Europa, Titan, and Pluto—places so cold that water is basically a kind of rock—only exist as they do because they formed beyond the frost line. This has led to the old saying:

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Okay, maybe that’s not an old saying, but I really wanted this to be a holiday-themed post.