Procyon: A System in Chaos

Procyon (bright spot) showing it’s white dwarf (Procyon B) and the 40 year orbit they have around each other. 1.7 billion years ago Procyon B was a red giant.

While Thalassa is a fictional planet, the science of the Procyon system in SOT is based on real research and our current understanding of stellar evolution and binary star systems.

Procyon: A Binary Star System

Procyon is the 8th brightest star in the night sky and thus a highly visible star. Together with Sirius (the brightest) and Betelgeuse (11th brightest), it is part of the Winter’s Triangle. Only 12.46 light years away from us, Procyon is in our close stellar neighborhood and is the 15th closest star to earth. It is a double star with a faint but invisible to the eye white dwarf companion, the remains of a bigger star.

Stars are classified by their mass and temperature, which determines their color. Earth’s sun is a yellow G-star while Procyon (Procyon A in the binary system) is a slightly larger yellow-white F-star (1.5 times our sun’s mass) . As such, it is seven times brighter than our sun. The light on Thalassa would be yellow-white, not yellow, as it is on earth, and light-trapping photosynthetic organisms may use different pigments and hence display different colors than plants on earth (Kiang, 2008). This is why the fronds and lichen-like creatures on Thalassa are yellow, orange, and red, not green.

F-stars also emit 2-7 times the amount of cell-damaging ultraviolet light (UV) as our sun, which would likely inhibit the development of life on land. However, seawater is a good shield against UV light, especially in the deep sea, so ocean creatures are protected from UV.

Because bigger stars burn brighter and hotter they die much faster than smaller stars, Procyon A will only last two billion years compared to our sun’s 10 billion year life span. Since it is now 1.9 billion years old it will transition to a red giant in the next 10-100 million years.

The size of Procyon A & B relative to earth and our sun. Source.

Procyon A’s white dwarf, Procyon B, was once a very bright bluish B-type star 2.6 times the mass of our sun. Because it burned hotter, it turned into a red giant after a billion years before collapsing into a small white dwarf, smaller than Earth. On Thalassa, Procyon B would appear twice as bright as a full moon.

Procyon’s neighbors’ red giant phase

When a star runs out of hydrogen fuel to fuse into helium within its core it begins to collapse while the outer atmospheric envelope expands. After a few million years the red giant ejects its outer layers then collapses into a white dwarf. Procyon B went through these stages about a billion years prior to the setting for SOT. During the end of Procyon B’s life it would have ejected a significant amount of ionized radiation and UV light into the region which would had a disruptive effect on the asteroids and comets around the binary star system.

Rain of Debris

Artist’s illustration of comets raining down on a planet. Source.

During the early life of all solar systems, debris remains from planet formation which includes asteroids and comets. Asteroids are made of metals and rocky material and formed closer to the star, where it is too warm for ices to remain solid. Comets are made up of ice, dust and rocky material and are formed farther from a star where ices does not melt. As comets approach a star their ice melts and vaporizes to form a tail.

Our solar system, and likely similar systems with planets, went through several hundred million years of collisions from asteroids and comets called the late heavy bombardment period. Most of the craters in the moon, and those visible on other planets, satellites, and asteroids, were created during this time period which occurred 4.1-3.8 billion years ago (Gomes et al., 2005). Few of these craters are visible on earth due to erosion and plate tectonics, but there are some.

It is likely other solar systems had similar episodes of intense collisions within 500-800 million years of their formation, such as Procyon. In addition, in SOT, it is postulated that when Procyon B’s red giant blasted off its atmosphere, it disrupted the asteroids in the system, and the comets in its Oort Cloud, causing a second period of intense bombardment. As a result, Procyon is envisioned as displaying numerous comet tails, like spokes in a wheel, and the frequency of asteroid and comet collisions with Thalassa is relatively high.

Artist’ illustration of comets plummeting a solar system as envisioned for Procyon and Thalassa. Source: NASA.

Procyon’s Orbit

As in any binary system, Procyon A and B orbit each other, and with a period of 40.8 years. Their orbit is elliptical (not a circle) and the distance between the stars varies between 8.9 AU and 21.0 AU. One AU is the distance from the earth to the sun, about 93 million miles. At their closest they are about the same as the distance between us and Saturn; at their farthest about the distance between us and Uranus.

Orbit of Procyon’s white dwarf around Procyon A. Source.

Procyon A and B were at periastron (their closest) in 1967, 2008, and will be again in 2050 and on May 15, 2090 when Syzygy between the white dwarf and two moons occurs in SOT. This is one reason the book’s setting is during 2089-90 as it corresponds with the actual peristron’s date..

References and Further Reading:

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