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A Small Red Star: Ross 248

by Les Johnson and Ken Roy

“For my part, I know nothing with certainty, but the sight of the stars makes me dream.”
—Vincent van Gogh

When you are outside on a dark night and the skies are clear, the sky bursts forth in a majestic display of countless stars and a few planets. When you look at those stars, your eyes are seeing the light from distant suns that has been traveling through space for years, decades, centuries, and perhaps millennia. Many of those stars are just like our own sun, classified by astronomers as a yellow “Class G” star, and not atypical among many others you might see. Some are larger or smaller, some are hotter, others cooler, and you might think that the stars you view are the norm for those that make up our Milky Way galaxy—and you would be wrong.

A color-composite image from the Sloan Digital Sky Survey
showing many red dwarfs (all the reddish looking stars).
Credit: Sloan Digital Sky Survey

Most stars are much smaller than our sun and not visible to the naked eye. They are red dwarfs, and not even one can be seen from the Earth without the aid of a telescope. Red dwarfs, also called M-type stars, are the most numerous type in the universe, representing some 75% of all main sequence stars. M-type stars are very small and much cooler than our sun. They emit very little light, sometimes as little as 1/10,000 that of the sun, and that light is shifted far into the infrared. Because they burn through their hydrogen so slowly, they will exist on the main sequence for up to a trillion (that is a trillion, with a ‘t’) years. By contrast, our sun has a duration on the main sequence of around ten billion years. Recent discoveries proved that red dwarf stars can possess planets, and in the case of the red dwarf star known as Trappist-1, seven are terrestrial, or Earthlike, planets. Because these red dwarf stars are small, ranging in mass between 7% to 50% that of our sun, their planetary systems are also small. For example, the entire Trappist-1 system, if superimposed on our solar system, would fit nicely within the orbit of Mercury. Red dwarf stars have habitable zones, meaning that some of the planets orbiting them are at such a distance from the star that they can have liquid water, but such zones are close enough to the star that planets within it are probably tide locked—with one side always facing the star and the other always facing darkness. (Tide locked planets take the same amount of time to spin once about their axis as they take to complete one orbit around their parent star, making the star appear to hang motionless in the sky. Our moon is tide locked with the Earth, which means we only see one of its two sides.)

Many red dwarf stars undergo unpredictable, dramatic increases in brightness, during which they are thought to throw off energetic particles and electromagnetic radiation in what are popularly known as solar flares. These flares sometimes hit the orbiting planets and could do great damage to any biospheres there.

In the Milky Way Galaxy, about three-fourths of the estimated 100 billion stars are red dwarfs.

Ross 248

First catalogued by astronomer Frank Ross in 1926, Ross 248 is a nondescript red dwarf star located about 10.3 light years (LY) from Earth in the constellation of Andromeda. Ross 248 is a cool, dim star with a mass roughly 14%, a radius 19%, and a luminosity 0.2% that of our sun.

Although it has been studied by numerous researchers, no planets have been detected there. This does not mean the star doesn’t have planets, just that any planets present might be oriented such that they are hard to detect with our current methods. Astronomers are confident that it doesn’t have any large planets (Jupiter’s size or larger), brown dwarfs, or other stars as companions. The star seems to have a slightly higher metallicity ratio (the ratio of iron to hydrogen) than our sun, indicating that it is at least as rich in metals as our solar system. It is thought by some to be a young star at 2.6 billion years, roughly half the age of our sun, but with a life expectancy that exceeds our sun by hundreds of billions of years.

Ross 248 also has the interesting property of a relative motion such that it is moving toward our solar system. In 30,000 to 40,000 years, it will be the closest star to Earth at an estimated distance of some 3 LY—replacing another red dwarf, Proxima Centauri, as the closest star to the Earth.

Ross 248 is the very real setting for our Baen anthology, The Ross 248 Project. Rather than start completely from scratch inventing a stellar system, we chose to loosely base the setting for the anthology on the aforementioned Trappist-1 star system, which was discovered to have a host of terrestrial planets in 2016 and 2017.

The Trappist-1 system is located 39 LY from Earth in the constellation of Aquarius and has characteristics very similar to Ross 248. The system has seven confirmed planets ranging in mass from 0.3 to 1.2 Earths, with gravities ranging from similar to Mars at a minimum to slightly higher than Earth at a maximum. This star even has its own website with many more details available at http://www.trappist.one/.

We know so much about this small star and its planets because of a very unusual alignment. Its plane of the ecliptic, if extended, would cut through our solar system. Thus, Trappist’s planets pass between us and their parent star, slightly dimming it each time they transit, allowing researchers to measure the planet’s mass, size, period, and distance from the star. This allows us to make calculations to determine each planet’s likely gravity, temperature, and to some extent even atmospheric composition. If Trappist-1’s plane of the ecliptic was tilted even a few degrees, then the planets would not transit the star (from our perspective) and we would have no idea that such a solar system existed. There is another planetary detection technique that allows us to watch the star being pulled to and fro due to gravity from a large (and otherwise invisible) planet via a periodic Doppler shift in the spectral lines of the host star, but multiple small planets make this technique difficult to implement; plus, this technique can’t measure the non-radial part of the star’s movement. The conclusion is that currently, it is very difficult to identify the planets of a typical red dwarf star.

Is it reasonable to infer that Trappist-1 is a unique star, or could it be a very typical red dwarf with the single exception of its atypical orientation? We have found other red dwarf stars with planets, so it is not unreasonable to assume that many red dwarf stars have planetary systems with multiple rocky planets. If Trappist-1 can, then so might Ross 248.

Creating A Fictional Planetary System for The Ross 248 Project

Inspired by the discussions at the biannual gatherings of the Interstellar Research Group (www.irg.space), we decided to create a shared universe anthology of original science fiction stories and “science behind the fiction” essays that would describe what happens at the conclusion of a realistic interstellar voyage, when future human travelers would face very real challenges associated with either adapting to life on alien worlds or adapting those worlds to accommodate human habitation—a process called terraforming.

In creating this universe, we (the editors of the anthology) had to take Ross 248 and imagine what a planetary system there might be like based on the information gleaned thus far about the Trappist-1 system.

Ross 248 is about 50% more massive than Trappist-1, so its planetary system would be larger as well. This was accomplished by moving the inner planet out until it had roughly the same equilibrium temperature as the inner planet of Trappist-1. With the Trappist-1 system, each subsequent planet, on average, was 1.3 times the orbital distance of the previous planet. This rule was then applied to the Ross 248 planets to determine their orbital distance from the star. Then the mass and radius of some of the planets were “adjusted” to better serve the plot needs of the anthology and to avoid charges that the authors completely plagiarized a stellar system.

Knowing details of the star, a planet’s mass and distance from its star, it was then possible to calculate the orbital period, the solar constant at the planet, the planet’s equilibrium temperature, and the angular size of the star as viewed from the planet. Each of these are described in more detail below.

Next, each planet’s radius was assigned. The planets at Trappist-1 all seem to be rocky planets with a fair amount of water resulting in a low planetary density, so this was duplicated at the fictional Ross 248 by varying the planetary radii to achieve the required density. Given these details it is possible to calculate the surface gravity. The results of this effort are compiled in Table 1.

The first column is the planet’s designation. Ross 248, the star, is Ross-248a, the innermost planet is then Ross-248b, and so on with Ross-248h being the outermost one. Masses are in Earth masses. Orbital radius is in units of millions of kilometers. Note that the orbital radius of Ross-248h is 19,320,000,000 meters while the orbit of the planet Mercury is three times that. Ross 248 is a tiny solar system with travel times measured in days or weeks. The next column is the orbital period, how long it takes for the planet to circle its star, in units of Earth days. A “year” on Ross-248b takes about 3 days. The next columns are the planetary radius in Earths, the surface gravity measured in Earth gravities or “g,” and the length of the solar day in Earth days. A solar day would be the time between sun rise until the next sun rise. We assumed that the planets are either tidally locked or spin very slowly.

The next column is the solar constant as seen from the planet in units of watts per square meter. Note that the solar constant for Earth is, on average, 1361 watts per square meter. The last column is the equilibrium temperature of a small, dark metal sphere in the same orbit as the planet in units of degrees Fahrenheit. This assumption ignores such things as atmospheres, the greenhouse effect, or internal heating, meaning that the actual planetary temperature could be significantly different that the indicated equilibrium temperature, but it is a start.

Table 1 is simply the bare bones of the Ross 248 system. Each planet needed to be fleshed out and given its own character. Your esteemed editors attempted to do just that, and the results are described below.

The Fictional Planets at Ross 248

Ross-248b (Aeneas) and c (Cupid), the two innermost planets, have thick atmospheres of carbon dioxide (CO2) and water (H2O) and are as hot as Venus. They are tidally locked with their parent star and their atmospheres circulate at a high-speed, making them uninhabitable and difficult targets for terraforming. Cloud cities, as we may someday build at Venus, are possible and could mine the atmosphere for trace gases such as He-3 (valuable as fusion fuel) and nitrogen (valuable for terraforming). A cloud city on Ross-248b would experience almost exactly 1.0 Earth gravity. Because these worlds resemble Venus, they are named after the children of Venus in Roman mythology.

Ross-248d (Poseidon’s World) is the third closest to the star. It is a water world with no dry land and a thin nitrogen and CO2 atmosphere, roughly what you experience at Pikes Peak, with clouds covering most of the planet. The gravity is a comfortable 0.93 g. The planet has no life in its single, world-spanning ocean that ranges from 20 to 35 kilometers deep. At that extreme depth, the pressure varies from 26,000 to 46,000 pounds per square inch (psi) and would thus be very cold. The water near the surface has an average temperature of 60oF and, while salty, is less salty than Earth’s oceans. The planet is semi-tidally locked and rotates very slowly, having a solar day equivalent to 4.74 Earth days. This planet is named Poseidon’s World because of its single large ocean. The ocean’s water has a pH of 6.6, which is slightly acidic, and needs to be converted to a pH of 8.1 for Earth life to survive and thrive. There is no land, but floating cities could be constructed for humans. Once the chemistry has been adjusted, Poseidon’s Ocean might become a home for Earth-based marine life.

The fourth planet out, Ross-248e (Eden), is in the middle of the habitable zone and is the most Earthlike planet in the system. It has an oxygen atmosphere and indigenous life, with two large polar ice caps containing massive amounts of ice. The atmosphere is slightly thinner than Earth’s and in addition to oxygen, contains nitrogen and enough CO2 to provide a useful greenhouse effect making the average temperature just above freezing. Gravity is 89% that of Earth. The equatorial region is a mix of ocean and small continents with temperatures that are always above freezing. Away from the equatorial region, the climate is cold enough to get heavy snow in the winter that then melts in the summer. Keep in mind that the year on Ross-248e is slightly over 11 Earth days. There is life there, some reminiscent of the dinosaurs, but there is no indication of intelligent life or any previous civilization. The planet rotates quickly, with a solar day being equal to 31.2 hours. This planet is named Eden because, at first glance, it seems to be a paradise.

There are ethical and compatibility issues with introducing Earth life into this alien biosphere. Should this world be terraformed or left alone? It must certainly be studied. The life on this planet is carbon-based and uses thirty-two amino acids, fifteen of which are also utilized by Earth life. It has an alien DNA system completely different from Earth life, suggesting that it developed completely independently. Several scientists studying it at the cellular level have suggested that it gives every indication of having been engineered.

Ross-248f (Nordheim), the fifth planet, has a gravity like Earth. It was named by a man who remembered pictures of his parents’ hometown in Norway back on Earth. Nordheim is a frozen world, covered in ice with a few mountains rising high above the surface. The atmosphere is nitrogen and carbon dioxide with an average temperature of -58o F. There is no indication of life. Forty kilometers beneath the ice layer lies a liquid water layer several hundred kilometers deep, heated by the planet’s molten core and the hot gas of its subterranean volcanoes.

There is no straightforward way to terraform this world. If it is warmed, then the ice will melt and transform it into a water world. Besides, doing so would require a LOT of heat. The consensus is that it is a viable candidate for subterranean space settlements that might one day be common on the moons of Earth’s gas giants. Exploring the subterranean ocean could be interesting, but it is very cold, dark, salty, and under high pressure.

Ross-248g (Frigus) is the sixth planet, with a gravity about 67% that of Earth. It too is a frozen world, covered in a thick layer of ice and having every indication of possessing a subterranean ocean just like its planetary neighbor, meaning that it probably has a molten core as well. Ross-248g has an average surface temperature of -107o F and a solar day equal to 15 Earth days. It was named Frigus after the first human to walk there had a suit malfunction and almost froze to death.

Ross-248h (Alexa’s World) is the seventh planet and has a gravity only 64% that of Earth, with a solar day equal to 16.6 Earth days. It is very cold, with an average temperature of -172o F and a very thin nitrogen atmosphere. The planet has been impacted by many comets and asteroids, affording access to metals and other raw materials near its surface. Space settlements can be built under the surface of this world, but rotating structures are necessary to provide the required gravity for humans. This world has no liquid ocean, and the core is solid.

It is also the home of Alexa’s Oddity, or sometimes just “the Oddity.” First observed by Alexa Prandus, the Oddity is a large flat plane located on top of a tall stone mountain. The large plane, which looks like it was created by shearing off the top of the mountain, is surrounded with odd features. When people first landed there, they noted that the level plane turned out to be made of vitrified stone and surrounded with the ruins of long abandoned structures, also made of vitrified stone. This was clearly a long-abandoned alien facility. After a careful search and much digging, nothing was found to indicate who built it. No artifacts or any alien technology was discovered. It had apparently been abandoned 10,000 to 20,000 years ago, and whoever abandoned it went to great trouble to leave nothing behind. Alexa was the first human to walk this world, so she had the right to name it, but she refused. The leadership then simply named it Alexa’s World.

Gravity is an underutilized factor in science fiction. For the anthology’s timeline, it was stated that humanity had divided into two branches. One, like us, are termed “normal” humans and require 0.85 to 0.90 g to maintain health. Adults can handle no gravity for a few days or weeks before health issues begin to manifest, but pregnant women and children require this level of gravity full time. The second branch of humanity is termed Cerites, because they adapted themselves to thrive on the asteroid Ceres. They are thus well adapted for life in space and are highly resistant to radiation. Lack of gravity doesn’t affect them, but they can’t function when gravity exceeds 0.1g. This makes the surface gravity of the various worlds relevant to the story. It is also why we had to give Ross-248h a moon.

Alexa’s World is the only planet in the Ross 248 system to have a moon. Larger than Ceres, the moon has a gravity of 0.08 that of Earth, which is ideal for the Cerites, and this is where they established their base, Toe Hold. The moon is named, Liber, the son of Ceres in Roman mythology who was known as “the free one” and a god of viticulture, wine, fertility, and freedom. The first settlements there were constructed under its surface to provide shielding for radiation protection and some degree of thermal control. Liber and Alexa’s World are tidally locked with each other, making the orbital period of the moon the same as the solar day for the planet.

We also assumed the existence of a Kuiper Belt beyond Ross-248h with comets and asteroids, and a few dwarf planets, available for mining. We don’t know if red dwarf stars have Kuiper belts (none have been detected), but the fictional Ross 248 system has one.

Conclusion

Every reasonable effort was made to try to make this a realistic planetary system; one that the contributing authors could use not only as a setting, but as characters in their stories. The anthology editors also created a rough timeline of how humanity, and its children, ended up at Ross 248 and some of the dangers they endured and obstacles they overcame along the way. We also spent a lot of time thinking about starships, but that is a tale for another time.

Each story, though meant to stand alone, is linked to the overall timeline. There is no need to spoil the fun here—go read the anthology. Oh, and make sure to take time to look at the stars. Those you don’t see might be the most important ones out there.

Les Johnson is an author, scientist, and NASA technologist. His latest book, A Traveler’s Guide to the Stars (Princeton Press), describes how we might someday reach the stars. You may learn more about Les, his books, and his work by visiting his website: www.lesjohnsonauthor.com.

Ken Roy is a retired engineer who enjoys thinking about terraforming, space exploration, military history, transhumanism, and reading Baen books. He enjoys attending LibertyCon and talking to fans. Feel free to strike up a conversation. He also enjoys looking at the stars and dreaming of a positive future.

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