Tag Archives: exoplanets

Astronomy, Education

How to use ChatGPT to model exoplanet interiors as a lab for high school students.

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Like the introduction of hand calculators into the classroom in the 1970s, ChatGPT offers enormous promise but currently suffers from a variety of negative expectations. Some of the arguments against students using calculators in the 1970s classroom are being used today against ChatGPT. I think there are some applications that work very well if you consider ChatGPT to be an intelligent ‘hand calculator’ in the math and physical science classroom. Here is an example I came up with without much effort!

I. Student Pre-Requisite Knowledge

The following example requires students to work with Scientific Notation, calculating the volume of spheres and shells, and working with the mass:density:volume relationship.

II. Exoplanet Interior Modeling

Astronomers have discovered over 5000 exoplanets orbiting other stars. We call these ‘exoplanets’ so that they don’t get confused with the ‘planets’ in our solar system. From a careful study of these exoplanets, astronomers can figure out how long they take to orbit their stars, their distance from the star, their diameters and their masses. How do they use this information to figure out what the insides of these exoplanets look like? This activity will show how a simple knowledge of mass, volume and density provides the clues!

III. Mass, Density and Volume

Mass, volume and density are related to each other. If two things occupy the same volume but have different masses, the less-massive one will have the lower density.

Density = Mass / Volume.

Example 1: A Prospector had his sample weighed to be 20 grams, and its volume calculated by water displacement and found to be 4 cubic centimeters. If pure gold has a density of 19.3 gm/cc, is his sample actually gold or is it iron pyrite (density 5.0 gm/cc)?

Answer:   Density =  20 gm/4 cc =   5 gm/cc   so it’s iron pyrite or ‘Fools Gold’.

Example 2: A basic principle of physics is that light things of low density float on top of denser things. Why do you have to shake a bottle of salad dressing before you use it?

ChatGPT Query: There are five different liquids mixed together in a bottle. After 10 minutes they sort themselves out. The liquids are:   Olive oil ( 0.92 g/cc ), water ( 1.0  g/cc), molassis ( 1.4 g/cc) , vinegar ( 1.0006 g/cc), honey (1.43 g/cc). From bottom to top, how will the liquids separate themselves?

IV. Designing Mercury with a One-Component Interior Model

Mercury was formed close to the sun where only iron and nickel-rich compounds could condense into a planet. Let’s model Mercury and see what we discover. The actual mass of Mercury is 0.055 times Earth.

Step 1 – Use the formula  for the volume of a sphere V=4/3 pR3 and with a known radius for Mercury of Rm = 2.43×106 meters to get the volume of the planet of V = 6×1019 m3.

Step 2 – Calculate the mass of Mercury for various choices of density. Give the predicted mass for Mercury in multiples of Earth’s mass of 5.97×1024 kg.

Step 3:  Test your knowledge: For a density of 5000 kg/m3 and a radius of 2.43×106 meters, what is the mass of Mercury for these selected values? Give your answer to two significant figures.

Volume = 4/3p (2.43×106meters)3     =  6.0×1019 m3

Mass = 5000 x Volume =  3.0×1023 kg

Mase(Earth units) = 3.0×1023 kg /5.97×1024 kg  = 0.05 times Earth

Use ChatGPT to generate data for plotting. Enter this question into the window:

ChatGPT Query: A sphere has a radius of 2.43×10^6 meters. What is the mass of the sphere if its density is 5000 kg per cubic meter? Express your answer in units of Earth’s mass of 5.97 x 10^24 kg. Give your answer to two significant figures.

Repeat the ChatGPT query four times to generate a mass estimate for densities of 4000, 4500, 5000, 5500 and 6500 kg/m3. Plot these points on a graph of mass versus density and draw a line through the values. Which density gives the best match to the observed mass of Mercury of 0.055 Mearth?  (Answer: about 5500 kg/m3).

V. Designing Mars with Two-Component Models

Now we add two components together for planets that have a high density core and a lower density mantle. These would have formed farther out than the orbit of Mercury but with masses lower than than of Earth. The mathematical model consists of a spherical core with a radius of Rc, surrounded by a spherical shell with an inner radius of Rc and an outer radius of Rp, where Rp is the observed planetary radius.  Mathematically the model looks like this:

M = Dc x 4/3p Rc3 + Dm x 4/3p ( Rp3 – Rc3)

Draw a diagram of the planet’s interior showing Rc and Rp and confirm that this is the correct formula for the total mass of the planet where Dc is the core density, and Dm is the mantle density.

Test Case: An exoplanet is discovered with a mass of 5.97×10^24 kg and a radius of 6,378 kilometers. If the radius of its core is estimated to be Rc = 3,000 km and its core density is 7000 kg/m3, what is the average density of the mantle material?

Vc = 4/3p Rc3  =   4/3p (3000000m)3 = 1.1×1020 m3

Vmantle = 4/3 p Rp3 – Vc  =  1.1×1021 m3 – 1.1×1020 m3 = 9.8×1020 m3.

Solve equation for Dm:

Dm =  ( M – Dc x Vc ) /Vm

Dm = (5.97×1024 – 7000 x 1.1×1020)/9.8×1020 =  5300 kg/m3

Check your answer with ChatGPT using this query. A planet consists of a core region with a radius of Rc and a mantle region extending to the planet’s surface at a radius of Rp. If the planet is a perfect sphere with a radius Rp = 6378 km and Rc = 3000 km, with a total mass of 5.97×10^24 kg, for a core density of 7000 kg/cubic meters, what is the average mantle density? Give the answer to two significant figures.

Now lets use ChatGPT to generate some models and then we can select the best one. We will select a mantle density from three values, 2000, 3000 and 4000 kg/m3. The core density Dc will be fixed at Dc = 9000 kg/m3. We will use the measured radius for Mars of Rp = 3.4×106 meters, and its total mass of Mm = 6.4×1023 kg. We then vary the core radius Rc. We will plot three curves on a graph of Rc versus Mm one for each value of the assumed mantle density. Use this ChatGPT query to generate your data points.

ChatGPT Query: A planet is modeled as a sphere with  a radius of Rp=3.4×10^6 meters. It consists of a spherical core region with a radius of Rc surrounded by a spherical shell with an inner radius of Rc and an outer radius of Rp. The core of the planet has a density of 9000 kg/cubic meters. The radius of the core Rc = 30% of the planet’s radius. If the density of the mantle is 2000 kg/cubic meter, what is the total mass of the planet in multiples of the mass of Earth, which is 5.97×10^24 kg? Give your answer  to two significant figures?

Repeat this query by changing the mantle density and the core radius values and then plot enough points along each density curve to see the trend clearly. An example of an Excel spreadsheet version of this data is shown in this graph:

This graph shows solutions for a two-component mars model where the mantle has three different densities (2000, 3000 and 4000 kg/m3). The average density of mars is 3900 kg/m3. Which core radius and mantle density combinations seem to be a better match for Mar’s total mass of 0.11 Mearth for the given density of the mantle?

VI: Modeling Terrestrial Planets with a three-component interior.

The most general exoplanet model has three zones; a dense core, a mantle and a low-density crust. This is the expected case for Earth-like worlds. Using our Earth as an example, rocky exoplanets have interiors stratified into three layers: Core, mantle, crust. 

Core material is typically iron-nickel with a density of   9000 kg/m3

Mantle material is basaltic rock at a density of 4500 kg/m3

Crust is low-density silicate rich material with a density of 3300 kg/m3

The basic idea in modeling a planet interior is that with the three assumed densities, you vary the volume that they occupy inside the exoplanet until you match the actual mass (Mexo) in kilograms and radius (Rexo) in meters of the exoplanet that is observed. The three zones occupy the radii  Rc, Rm, Rp

We will adjust the core and mantle radii until we get a good match to the exoplanet observed total mass and radius. Let’s assume that the measured values for the Super-Earth exoplanet mass is Mp = 2.5xEarth = 1.5×1025 kg,  and its radius is Rp = 1.5xEarth = 9.6×106 meters.

Core Volume  Vcore = 4/3p Rc3

Mantle Volume  Vm = 4/3 p (Rm3 – Rc3)

Crust Volume   Vcrust =  4/3 p (Rp3 – Rm3)

So the total Mass = (9000 Vcore + 4500Vm + 3300Vcrust)/Mp

Rc ,Rm and Rp are the core, mantle and planet radii in meters, and the total mass of the model is given in multiples of the exoplanet’s mass Mp.

Let’s do a test case that we work by hand to make sure we understand what we are doing.

Choose Rc = 30% of Rp and Rm = 80% of Rp. What is the predicted total mass of the exoplanet?

Rc = 0.3 x 9.6×106 meters =  2.9×106 meters.

Rm = 0.8x 9.6×106 meters =  7.7×106 meters.

Then

Vcore =  4/3p (2.9×106)3 = 1.0×1020 m3

Vm =  4/3p ( (7.7×106)3 – (2.9×106)3) =  1.8×1021 m3

Vcrust =  4/3p ((9.6×106)3  – (7.7×106)3) =  1.8×1021 m3

Then  Mass = (9000 Vcore + 4500 Vm + 3300Vcrust)/Mp

Mass = (9×1023 kg + 8.1×1024 kg + 5.9×1024 kg)/1.5×1025 kg  =  1.0 Mp

Now lets use ChatGPT to generate some models from which we can make a choice.

Enter the following query into ChatGPT to check your answer to the above test problem.

ChatGPT Query: A spherical planet with a radius of Rp consists of three interior zones; a core with a radius of Rcore, a mantle with an inner radius of Rc and an outer radius of Rm,  and a crust with an inner radius of Rm and an outer radius of Rp=9.6×10^6 meters. If the density of the core is 9000 kg/m^3, the mantle is 4500 kg/m^3 and the crust is 3300 kg/m^3, What is the total mass of the planet if Rc = 30% of Rp and Rm = 80% of Rp? Give your answer for the planet’s total mass in multiples of the planet’s known mass of 1.5×10^25 kg, and to two significant figures.

Re-run this ChatGPT query but change the values for the mantle radius Rm and core radius Rc each time. Plot your models on a graph of   Rc versus the calculated mass Mp on curves for which Rm is constant. An example of this plot is shown in the excel spreadsheet plot below.

For example, along the black curve we are using Rm=0.8. At Rc = 0.5 we have a model where the core extends to 50% of the radius of the exoplanet .The mantle extends to 80% of the radius, and so the crust occupies the last 20% of the radius to the surface. With densities of 9000, 4500 and 3300 kg/m3 respectively, the Y-axis predicts a total mass of about 1.1 times the observed mass of the exoplanet (1.00 in these units). With a bit of fine-tuning we can get to the desired 1.00 of the mass.    But what about the solution at (0.3, 1.00) ? In fact, all of the solutions along the horizontal line along y = 1.00 are mathematically valid.

Question 1: The exoplanet is located close to its star where iron and nickel can remain in solid phase but the lower density silicates remain in a gaseous phase. Which of the models favors this location at formation?

Answer: The exoplanet should have a large iron/nickel core and not much of a mantle or crust. This favors solutions on the y=1.00 line to the right of x=0.5.

Question 2: The exoplanet is located far from its star where it is cool enough that silicates can condense out of their gas phase as the exoplanet forms. Which of the models favor this location?

Answer: The exoplanet will have a small iron/nickel core and a large mantle and crust. This favors models to the left of x= 0.5.

So here you have some examples for how ChatGPT can be used as an intelligent calculator once the students understands how to use the equations and is able to explain why they are being used for a given modeling scenario.

I would be delighted to get your responses and suggestions to this approach . Just include your comment in the Linkedin page where I have posted this idea.

Astronomy

Exoplanet Update!!

An artist’s impression of an exoplanetary system as seen from the surface of an exomoon. Image credit: IAU/L. Calçada.

The last time I discussed exoplanets in this blog was in 2017 with my essay ‘Exoplanets Galore‘, but I think we can all agree that a lot has happened since then!

Here’s the bottom line by March 2023 if you don’t want to read further.

Total exoplanets: 5,312 confirmed out of 9,343 candidates

Total in Habitable Zone: 214 exoplanets of all sizes

Total Earth Analogs: 23 the size of Earth in their Habitable Zones

Number of directly imaged exoplanets: About 30.

Number of atmospheres detected: 11 so far: Water, carbon dioxide, methane, hydrogen, helium and no biosignatures like oxygen, nitrogen.

Planets with magnetospheres: 1 so far: HAT-P-11b

Closest Earth Analog: Proxima Centauri b at 4.2 light years. (probably lifeless due to frequent flares from star). Gliese 1061 b, c,d at 12 light years. A planetary system with multiple Earth-sized candidates in HZ.

Closest Earth Analog around sun-like star: Kepler 452b, 1,400 light years from Earth orbiting G-type star. It is 5 times the mass of Earth and has twice the surface gravity. Probably between a terrestrial and Neptune-type surface with large ocean.

Searches in Progress: TESS was launched in 2018 and will operate until 2025. It will search the 200,000 brightest stars in the sky and hopefully find ‘thousands’ of new exoplanets using the transit method. So far it has found 6,386 candidates and 326 confirmed exoplanets. Gaia was launched in 2013 and will also last until 2025. So far, Gaia has found 18,383 candidates and has verified 73 exoplanets. Meanwhile there are over 43 ground-based major observatories with exoplanet detection programs mostly designed to verify candidates spotted by satellite studies.

Now let’s dig into the details!

According to NASA, by March 30, 2023 there are now 5,312 confirmed exoplanets, among 9,343 candidates, including 3,981 multiple-exoplanet ‘solar systems’. These confirmed exoplanets include 195 that are ‘terrestrial’ or Earth-sized, and 1,605 that are ‘super-Earths’ up to 5 times bigger than Earth. According to the European, Extrasolar Planet Encyclopedia (EPE) as of March 31, 2023 lists 5,346 exoplanets in 3,943 planetary systems, and 855 multi-planet systems.

The NASA catalog is searchable but very bare-bones. It only gives name, size and distance. The Extrasolar Planet Encyclopedia ( EPE), however is also searchable but in many more fields including the exoplanet’s radius, period and distance from its star.

First a bit of terminology.

Habitable Zone (HZ), also called the Goldilocks Zone, means the region surrounding a star where the temperature of an exposed surface with no atmosphere, is between the freezing point of water and the boiling point of water where life could supposedly exist. Of course you can’t have liquid water on a planet with no atmosphere, so these distances are lower limits. If the planet has a warming Greenhouse atmosphere dense enough for water to exist it can be farther from the star than these limits because the surface is warmed to a higher temperature. But it is a good first guess for the size of this zone without making any assumptions about atmospheric composition. By the way, Earth is right in the middle of our Sun’s HZ. Care has to be used in using this in the seach for life because even exoplanets that seem too cold to sustain liquid water could have liquid oceans under a thick icy crust like the moons of Jupiter.

Earth-sized means that the exoplanet is very close to our Earth in SIZE, meaning diameter, which means a radius of about 6,300 km. It also means that it can be found anywhere both inside and outside the HZ. Care has to be taken in using this as a search for life indicator because the moons of Jupiter-sized exoplanets can be Earth-sized like Titan in our own solar system, and tidal energy could keep their interiors warm enough for liquid water.

Earth-like means that the exoplanet is not only Earth-sized but inside its star’s HZ. These are also called Earth Analogs or Potentially Habitable Exoplanets.

Habitable Zone exoplanets

The very first thing that you or I would want to know is, how many of the 5,300+ exoplanets are in their HZs? Although a good estimate is about a few hundred, the exact answer is not as straight-forward as you might think.

Exoplanets are often found in elliptical orbits so some of these may only spend part of their ‘year’ in the HZ and most of their time too hot or too cold to support liquid water. To make matters worse, because stars evolve over time and become brighter, the HZs around every star start out close to the star when the star is young but slowly drift further away from the star as it ages. A planet formed inside the HZ may find itself outside the HZ as it gets older. In our solar system, Venus started out inside the HZ of the sun when it was formed 4.5 billion years ago, but now finds itself just inside the HZ today as a much hotter and inhospitable Earth-sized world. The range of distance during the entire lifetime of the star where HZ conditions exist is now called the Continuously Habitable Zone. Our Earth will leave this zone in another 7 billion years, while Mars will find itself in the comfortable middle of this zone by then.

Neither the NASA nor the EPE catalogs explicitly give statistics on this sub-category because the exact location of the HZ for each star depends on some assumptions including orbit shape, age of star, surface reflectivity, and Greenhous gas content. None of these ‘official’ catalogs wants to offer an official count because it could be ‘incorrect’ or worse-still, meaningless.

According to the Habitable Zone Gallery maintained by astronomers Stephen Kane and Dawn Gelino, their March 2023 catalog includes 4,628 exoplanets with known orbits. The figure below shows in green that only a total of 214 spend more than half their ‘year’ inside their star’s HZ. These include all types of exoplanets not just Earth-sized ones.

Image credit : HZGallery.org.

The Search for Earth Analogs.

How many exoplanets are both Earth-sized and in their star’s HZ? Depending on the details there are up to a few dozen that seem very promissing.

Encyclopedia Britanica says 40 as of March 2023. The searchable Habitable Exoplanets Catalog gives 23 Earth-sized and 39 super-Earths (3-10 times Earth mass) for a total of 62 habitable worlds by January 5, 2023. One graphical summary by Chester Harman gives 13 potentially habitable exoplanets as of March 2022 when stellar evolution is factored-in. So, lets take the charitable view and use the Habitable Exoplanets Catalog tally of 23 Earth-sized and 39 super-Earths.

The habitable zone for a range of stellar temperatures, showing Venus, Earth, Mars, and a selection of potentially habitable exoplanets. (image credit: Chester Harman)

Well first of all, the super-Earth exoplanets are problemtical because they are larger and more massive than Earth. They have a lower density so many astronomers suspect that these are Water Worlds. If you had placed Neptune in the sun’s HZ at the time of formation, instead of being a planet with a thick icy mantle on top of a rocky core the size of Earth, it would have had a thousand-kilometer-deep water ocean on top of a rocky Earth-sized core. You could have life in a deep ocean, of course, but with no solid surface on which life could emerge and evolve. It is hard to understand how ‘fish’ would have created telescopes or even known that the rest of the universe exists at all.

Some of these super-Earths closer to the size of our planet could have enormous oceans covering their surface but with diminishing land areas. For future explorers, these exoplanets would still be massive enough that we would never be able to visit the small islands on their surfaces and return to space because their escape velocities are so high.

The closest Earth Analogs.

We are obsessed with finding the closest because these would be the easiest targets for future interstellar probes to visit within a human lifespan of travel. The current catalog lists quite a few of these but they all orbit red dwarf stars. TheTRAPPIST-1 system contains TRAPPIST-1e, f and g — all located in the habitable zone of the star. The M8V red dwarf star is 39 light years from Earth. Unfortunately, different studies have come to different conclusions on whether any TRAPPIST-1 planet can retain substantial amounts of water. Because the planets are most-likely synchronized to their host star, water could become trapped on the planets’ night sides and would be unavailable to support life.

Meanwhile, Kepler 442b located 1,200light years from Earth is only 2-3 times the mass of Earth and is in the HZ around a K-type sun-like star. It has a temperature of 233 K (−40 °C; −40 °F) and a radius of 1.34 REarth. Because of its radius, it is likely to be a rocky planet with a solid surface. The mass of the exoplanet is estimated to be 2.36 MEarth. The surface gravity on Kepler-442b would be 30% stronger than Earth, assuming a rocky composition similar to that of Earth.

Based on the observations available by 2013, statistically, there should be nearly 9 billion habitable Earth-sized planets in our Milky Way. A 2020 estimate places this at about 6 billion exoplanets orbiting sun-like stars. A 2019 study places this at 10 billion habitable exoplanets orbiting the stars in the Milky Way of which one in every four G-type stars have habitable planets. A bit of math tells us that the volume of the Milky Way is about 17 trillion cubic light years. If you scatter 10 billion habitable exoplanets throughout this volume, you get 17 trillion cubic light years/10 billion exos = 1,700 cubic light years/exoplanet. That means the average distance between them is about 12 light years, which is very promissing!

Within 100 light years of the Sun there are 512 of these sun-like stars so there could be as many as 128 habitable Earth-like exoplanets yet to be discovered! These would be close enough to Earth to consider sending fast, unmanned spacecraft to visit them and check for lifesigns first-hand.

Astronomy, Biology, Space Travel

Exoplanets Galore!

***This Blog was updated in 2023 with new data. Visit Exoplanet Update. 

The year was 2001 – The first of the new millennium. It was also the year astronomers reached a historic milestone: They had catalogued more planets orbiting distant stars than the eight we knew about in our own solar system!

The first of these was discovered in 1988: A Jupiter-sized world orbiting the star Gamma Cephi A at a distance of 45 light years from our sun. Since then, well over 3,600 ‘exo’planets have been discovered using many different detection methods both on the ground and in space. We are truly living in a very different age than we experienced only a few short decades ago. We no longer have to speculate whether other planetary systems exist across the universe. We now have the technology and a growing catalog of examples to prove our solar system is not alone in the universe!

One of these detection methods is the Transit Method. As a planet passes in front of its star as viewed from Earth, the brightness of the star dims by an amount equal to the ratio of the planet’s circular area to the star’s circular area. For example, a Jupiter-sized planet has a diameter of 143,000 km while a sun-like star has a diameter of 1.4 million km, so the ratio of their areas is 1/100. As this exoplanet transits the disk of its star as viewed from Earth, the brightness of the star will dim by 1%. By measuring the time between successive transit ‘dips’ you can deduce the orbit period of the planet. From the orbit period and the mass of the star you also obtain the distance between the star and the planet. Once you have this information, you can estimate the surface temperature of the planet and its average density (rocky planet or gas giant). In the example below, the orbit period is 4.887 days and from the amount of dimming ( 0.7%) the ratio of their areas is 1/142, and planet’s diameter is 1/12 the diameter of its star.

To take advantage of the transit method on a large scale, NASA launched the Kepler Observatory in 2009. Using a super-sensitive digital camera, it took a picture of the same star field in the constellation Cygnus every minute and captured brightness information for over 150,000 stars similar to our sun. Over the course of its survey, now in its eighth year, it has discovered 4,496 exoplanet candidates of which 2,335 have been verified by independent study. These statistics now show that virtually all stars in the sky have at least one planet in orbit around them, and about 1 in 20 have Earth-sized worlds!

What was entirely unexpected was the diversity of exoplanet types, and orbits about their parent stars. Our solar system offered as templates the small rocky Earth-sized worlds of the inner solar system, the two gas giants (Jupiter and Saturn) and the two ice giants (Uranus and Neptune), but among the thousands of worlds discovered so far, a vaster array of possibilities have been found.

There are super-Earths over three times as large as our world apparently fully covered by deep oceans (Kepler 22b). There are hot-Jupiters that orbit their stars in a matter of hours, and swelter at temperatures of thousands of degrees (51 Pegasi b). Some planets have ‘water cycles’ in which silicate rock evaporates from their surfaces, condenses in clouds, and then rains droplets of lava back to the surface (COROT-7b, Alpha Centauri Bb, Kepler 10b). The cloud-shrouded super-Earth GJ 1214b is so hot that its clouds could be made of zinc sulfide and potassium chloride! One exoplanet is so close to its star that it is literally evaporating before our eyes, leaving a huge comet-like tail of gas in its orbital wake (HD 221458b).

The thousands of exoplanets detected by the transit method are especially intriguing. From Earth, as the exoplanet passes in front of its star, some of the starlight passes through the exoplanet’s atmosphere. Various gases in the atmosphere absorb selected wavelengths of this light and leave their unique fingerprints behind for distant astronomers using spectroscopes to study. So far among the dozen or so worlds examined, atmospheres rich in water vapor, carbon dioxide, methane, sulfur and other common molecules have already been found. This figure shows the spectrum of the exoplanet Wasp-19b and signs of methane (CH4) and hydrogen cyanide (HCN) – a lethal mixture for humans to breathe! Future ground and space-based observatories will be able to detect the molecules in thousands of exoplanet atmospheres, but this is no idle scientific pursuit. Living systems on a planetary scale sculpt their atmospheres by creating free molecular oxygen, so if we ever detect an exoplanet atmosphere rich in oxygen, it will be a major discovery of life in the cosmos beyond our own Earth.

Another aspect of the search for Earth-like worlds is to find exoplanets about as large as Earth that orbit their stars in what is called the Habitable Zone (HZ). In this range of orbital distances from the exoplanet’s star, the surface temperatures would allow liquid water to exist. In our solar system, this zone is located between the orbits of Venus and Mars, and Earth is smack in the middle of it. Currently, the various surveys have identified 13 exoplanets that are not only Earth-sized but are within their star’s HZ. The closest of these is GJ 273b at a distance of 12 light years! But there are complicating factors to finding an exact twin to our Earth upon which we might also hope to discover a living biosphere.

If a planet in the HZ has too much carbon dioxide – a potent greenhouse gas – its temperature would be more Venus-like and it would be a desert world or worse. If the exoplanet had significant traces of common gases such as hydrogen cyanide or methane, it would be unbreathable for humans though some extremophile bacteria on Earth thrive in such environments.

Another thing to think about is that an Earth-like world could be in orbit around a Jupiter-sized exoplanet in its star’s HZ. Even though we do not directly see the Earth-sized world there could be several of them as satellite worlds of larger exoplanets. The Jupiter-sized exoplanet WASP-12b appears to have an ‘exomoon’ with several times the mass of Earth. We know of hundreds of Jupiter-sized exoplanets orbiting in the habitable zones of their stars. We can no longer discount the possibility that their exomoons may be Earth-like though currently undetectable.

So far we have had to detect and study exoplanets indirectly from transit and spectroscopic data, but in a growing number of cases we can actually directly see these worlds as they spin around their stars. In 2008, the bright star Fomalhaut was observed by the Hubble Space Telescope and revealed a small planet among the debris of its dense disk of gas and dust. In another instance, the young star HR 8799 was observed by the Keck Observatory in Hawaii and revealed four massive planets (HR8799 b, c, d and e) in orbit. This is only the beginning of direct-imaging studies as we enter a new era of exoplanet studies.

What will the future bring? The spectacular success of the NASA Kepler mission is just the beginning of new missions to come that will discover thousands of new exoplanets. The NASA, Transiting Exoplanet Survey Satellite (TESS) will be launched in 2018 and will perform a Kepler-like survey of the 500,000 brightest stars in the sky. This survey will double the number of known exoplanets and include hundreds of additional Earth-sized candidates. At the same time, the Webb Space Telescope will be launched and among its many research programs will be ones to study the atmospheres of known exoplanets and Earth-sized candidates.

Check back here on June 18 for my next blog!