Habitable Exoplanets


by Maddie Meagher

The idea of finding a planet like Earth is a very exciting one to me and many others. However there are many factors that go into just making a planet suitable for life, factors such as location, temperature, water, atmosphere, and many others. Today I’m looking at some factors that play role in finding habitable exoplanets, or Earth 2.0 candidates as I like to call them. The main one I’m talking about today is the habitable zone. The habitable zone is the area around a star that a planet can have liquid water. The habitable zone is different for every solar system and is dependent on the parent star. Too close to the parent star and expect to have your oceans be boiled off. Too far and your planet would a giant ball of ice. The data I’m using for this little project comes from a site called the Habitable Zone. The site’s main purpose is to catalog planets in habitable zones and planetary equilibrium temperatures as well as many other various traits of planets.




These are the boundaries for the habitable zone for our own solar system. The two estimated ranges for habitable zone models in our solar system are the Conservative model from 0.95-1.4AU and the  Optimistic model from .85-1.7AU (Note an AU is the average Earth-Sun distance).




What I wanted to compare was how the location of an exoplanet can affect the planet’s average temperature. To get my data for locations of exoplanets I looked at the optimistic model for the habitable zone. The optimistic habitable zone extends the inner/outer boundaries of a solar system by using the “Recent Venus”(closer to parent star) and “Early Mars”(farther from parent star) criteria. The more optimistic estimate refers to assuming the planet has the right atmosphere to help keep in cooler than it should be at the inner edge, and warmer than it should be at the outer edge. The picture above shows our own solar system’s habitable zone with the optimistic habitable zone being in dark green. For temperature I looked at periastron equilibrium temperatures or Teqb in the database I used. The periastron temperature is the average temperature of a planet when it is at it’s closest point to it’s parent star . It’s also important that a planet is well mixed. What that means that it has an atmosphere that can trap heat well enough and have the heat spread evenly across the planet’s surface. For context, our home planet Earth spends 100% of its time in the habitable zone, and is well mixed, with an average temperature of 290K.


Using the data from the Habitable Zone I made a graph comparing percentage of time spent in the THZO (the optimistic habitable zone,on the x axis) and the Teqb (average periastron temperatures in kelvins on the y axis). And for reference the blue dot represents where our own home planet Earth would sit on this plot. The results I found is that the more time a planet spent in the optimistic habitable zone (THZO) the more temperatures tended to be below at 500 kelvin, they also tend to fall into the 200-300 kelvin range which is habitable (300 kelvins being a nice warm 80.33 degrees Fahrenheit). This is especially true for those planets who spent 100% of their time the Optimistic habitable zone. Though I noticed three big outliers on the graph. One  is a planet at 1457.4 kelvin (HD 20782 b) and the other at 1547.9 kelvin (HD 80606 b). Both these measurements are above 1400 kelvins or 2060.33 degrees Fahrenheit! However these two planets only spent very little time in the optimistic habitable zone as well as having some rather eccentric orbits (which I show below). The last outlier (HD 43197 b) spent more than 75% of its time in the habitable zone however temperature managed to reach 735.4 kelvins. The one thing all these planets have in common is that during their orbits they travel dangerously close to their parent star. This may contribute to the high periastron temperatures these planets.


Caption for three pictures above: All three of the exoplanets above for part of their orbit travel dangerously close to their parent star which is most likely the cause of the high spikes in their temperatures seen on the graph above. HD 20782 b doesn’t even spend all of it’s orbit too close to parent star or in the habitable zone. HD 20782 b spends a part of it’s orbit on the outer edge of the planets habitable zone where I would expect it temperature to drop.

Sources used:






Disk Detective

by Maddie Meagher (a 2016 Adler Astro-Journalist)

Trying to find planets forming around stars can be quite a daunting task even with the best technology available. This is where a Zooniverse citizen science project called Disk Detective comes in. It’s main goal is to find planets around other stars as well as finding planets in the process of forming. Currently we know very little about how exactly planet formation takes place. What we do know is that planets form around their parent stars in rotating vast gigantic disks, made of various gases and large chunks of rock. What we’re looking for in Disk Detective are two of kinds disks, and both types of these disks are the signposts of the planet forming process.

MaddieP1f1 YSO disk
Maddiep1f2 Debris Disk                          

The data for Disk Detective comes from a survey from a NASA satellite mission called WISE (Wide-Field Infrared Survey Explorer). From 2010 to 2011 WISE created maps of the night sky in infrared wavelengths to look for theses disks. As stars with disks around them shine brightly infrared light due the dust in the disks, where a star all by it’s lonesome wouldn’t shine bright in infrared at all. The two major disks astronomers were looking for in these maps are YSO and Debris disks. YSOs have disks mostly made of gas where planets like Jupiter and Saturn can form. These disks are often less than 5 million years old and will tend to form in clusters. In the picture above for the YSO disk (HL Tauri) you can see where planets in development have begun to clear their orbits around their parent star. Seen by the empty bands in the disk.

On the other hand, Debris disks tend to resemble the Kuiper belt in our own solar system, however, on a more massive scale. A Debris disk’s age tends to be about 5 million years and older. They tend to be composed of more rocky and icy materials and they usually orbit around older stars. Rocky planets like Earth are believed to form out these disks by dust moats gathering around a star to form rocks. Collisions of the larger rocky objects eventually snowball in a rocky planet like Earth, Venus, or Mars!

Image: Distribution of infrared brightnesses (x-axis) for a sample of 84 stars. While most stars cluster around 1, a lot of the stars have a higher amount of infrared emission (further to the right on the x-axis). Stars with planets are shaded as dark gray, while stars without known planets are shaded with light gray. Although stars with known planets make up less than a third of the sample, four of the five stars with the highest infrared brightness have known planets.
Citation: Beichman et al.2005 Astrophysical journal 622: 1160-1170

Keep in mind, in the graph above stars with disks like HL Tauri are most likely not counted in stars with known planet category. As the bands you saw in the picture above are only indirect evidence of planets residing there.

While WISE has taken Thousands of pictures of the night sky to create the most powerful survey for dusty disks ever known, it does not change the fact stars surrounded by a disk can be rather difficult to spot. Stars with a disk aren’t the only objects in the night sky that glow bright in the infrared (ex: galaxies,asteroids,active galaxy nuclei). Even computer algorithms designed to automatically search for these disks are easily thrown off by these sources of confusion. This is why there is a need for citizen scientists to help classify these objects. So that we can make sure that what we’re really looking at stars with disks. Finding these disks and the birthplaces of planets has been a major quest of astronomers for the last three decades. So start classifying and make new discoveries!


Disk Detective Tutorial
Spectral Energy Distributions (SEDs)

Why Study Exoplanets?

By Caroline Binley

92,955,807 miles above Earth, the Kepler Space Telescope orbits our planet and observes light from close to 150,000 stars. Astronomers turn data from Kepler into graphs of light given off by celestial bodies over time. These graphs are called light curves.

transcb1For a better understanding of light curves, give the NASA graph (left) a glance. Position one shows a planet before it passes the star it orbits. In this position, Kepler observes the star’s normal brightness. In position two, the planet stars to pass between Kepler and the star. As a result, Kepler perceives less of the star’s light. In position three, the planet blocks as much of the star’s light as it can, and the lightcurve dips even further. Scientists work backwards from the low points they see on these graphs in order to identify exoplanets.

Exoplanets are planets outside our solar system. They either orbit other stars or travel the universe without a host star. So far, we’ve only confirmed 1,827 exoplanets, but astronomers have thousands more candidates to consider.

Zooniverse — a portal to citizen science projects ranging from physics to humanities — hosts Planet Hunters, which allows users to help find exoplanets through lightcurve analysis. But why do we care about finding these planets?

If nothing else, it’s cool. From dreaming up constellations to watching “Star Trek,” humanity has demonstrated its stargazing curiosity countless ways. Now we’re finally able to explore — at least from a distance — the worlds we’ve so long dreamed of. That’s my first, unabashedly geeky answer.

But of course, not everyone is so easily fascinated by these planets. Beyond wow factor, exoplanets are key to our understanding of how our Earth and solar system function. The eight planets that orbit the Sun make up a small datapool. As a result, there’s knowledge we have to look beyond our solar system to gather.

Exoplanets are often at different stages in their life cycles than Earth, and the solar systems they make up have different characteristics than our own. This diversity has taught us how our solar system could have looked. Some stars host larger planets, some have their planets distributed differently, and yet others have planets with more distinctly elliptical orbits. This diversity also teaches us about solar system formation. For example, solar systems with Jupiter-sized (big) exoplanets near host stars confirmed the theory that planets move during formation.

And, of course, exoplanets propel us towards answering what many consider the ultimate question: are we alone in the universe? We don’t yet have the technology to search for exoplanetary life, but that that doesn’t mean that life isn’t out there. As we start to measure which planets are habitable (since we don’t have a better way to define “habitable,” I just mean Earth-like) our search will narrow, and we might even be able to answer that ever-looming question.












Detecting Distant Solar Systems

by David Zegeye




Citizen science projects are projects that the public can get involved with on various topics ranging from humanities to astronomy. Zooniverse, which is an organization that offers various citizen science projects, has launched a new project called Disk Detective. In Disk Detective, users search for disks of dusty material around stars.

When looking at a star in infrared, which is a different wavelength of light than the light humans are able to see in, scientists may be able to see a disk orbiting around them. Disks are made of gas, dust, and debris that exist as a circular shape in orbit around a star and were formed at the star’s birth. There are two forms of disks that orbit around different stars: debris disks and YSO disks. The stars that debris disks orbit around are 5 million years old or older with the disks being mainly composed of rock and ice. YSO, short for Young Stellar Object, are young stars typically found in clusters and are about less than 5 million years old. Unlike debris disks, YSO disks are instead mostly made of gas similar to what makes up gas giant planets. YSO disks can lead to the emergence of a solar system while debris disks contain remnants of material that helped form its solar system.

Stars can emit light in various wavelengths, however, the disks that orbit them absorb the light and re-emit it in mainly infrared light, which makes the stars stand out because of all the infrared radiation that their disks emit.  Identifying potential stars that have these disks was one of the goals for the Wide-field Infrared Survey Explorer telescope, also known as WISE. However, WISE has collected too much data for scientists to analyze by themselves over the course of its mission. Due to this problem, scientists decided to open this project to the public for them to further help investigate this topic, which is why Disk Detective was created. In Disk Detective, users will be looking at images of objects in multiple types of light in order to determine whether or not the candidate satisfies the requirements to be a disk. The user selects characteristics from a list that matches up with the object that they see and their responses then get compiled together for scientists to analyze and eventually conclude whether or not the candidate fits the description they’re looking for. Scientists are asking the public to identify these stars instead of using computers because computers can’t properly determine what the object they’re looking at is since they lack the ability to make proper judgements of objects by their appearance and characteristics. Human eyes, however, are very precise when it comes to categorizing objects. This is very helpful for Disk Detective because every object that has dust looks like a blob in  images from WISE, so often looking in the optical can help you determine whether or not an object is a star or a galaxy by looking at the objects features such as cross patterns or spiral arms. These screen shots from Disk Detective help explain why the users look at objects in different types of light:


The object on the left is a candidate star with a disk observed in longer wavelength of infrared. The object on the right is the same candidate star observed in optical light, thus showing more defined characteristics of the star.


The object on the left is a candidate star with a disk observed in longer wavelength of infrared. The object on the right is the same candidate object but observed in optical light, thus revealing that the object is a galaxy and not a star!

The public can get involved in Disk Detective by going to diskdetective.org and searching for stars with potential solar systems. I’ll continue my adventures in Disk Detective and report back any new findings. Until then, see you!