In the first chapter of Genesis, God instructs mankind to “Be fruitful and multiply; fill the earth and subdue it” (Genesis 1:28). Some commentators say that the last part, “subdue it,” means “to exercise great care over.” It stands to reason that exercising great care includes learning as much as possible about our planet that allows us to flourish as God intended for his human creatures. Accordingly, scientific development of space technologies continues to reveal special features of our home planet which make that thriving possible.
Earth’s Features Allow for Beneficial Space Technologies
Hugh Ross’s book Improbable Planet explains in intricate detail how the composition, climate and the geophysical and biological history of Earth are fine-tuned for human civilization. But humans have done much more than exploit Earth itself. We have sent spacecraft to the Moon, to all the other planets, and beyond the solar system. This spacefaring capability has been an enormous benefit to human well-being.
Is there something different about our planet that makes space exploration possible? Could a civilization on a “potentially habitable” exoplanet find similar success?
To date, over 4,000 extrasolar planets have been discovered. Of these, certain types, such as super-Earths and some planets around M-stars, are thought to be potentially habitable, perhaps even hosting technological civilizations. That possibility has led some scientists to compare the spacefaring potential of those exoplanets to what has been achieved by our Earth-based civilization.
Super-Earths Make Getting into Orbit Nearly Impossible
Astrophysicist Michael Hippke found that getting a satellite into orbit from a super-Earth would require an exponentially more massive rocket than if launched from Earth.1 For example, on a typical super-Earth with a radius 1.6 times that of Earth, it would require a rocket approximately the mass of the largest ocean battleship in order to put the James Webb telescope into orbit. The atmosphere of a super-Earth would be denser and extend higher, making the rocket motor much less efficient compared to a flight from Earth. In addition, it would be very difficult to land and recover the massive first-stage booster, as SpaceX is doing with its Falcon rockets.
M-star Planets Make Interstellar Escape Nearly Impossible
Launching orbital satellites from planets in the habitable zone around M-stars (a common type in the solar neighborhood) would be somewhat comparable to that from Earth. However, Harvard astrophysicist Abraham Loeb and his colleague found that despite their much smaller host star, these planets require a much greater velocity in order to escape into interstellar space.2 That’s due to their close proximity to their star. The speed would be 50% greater than from the orbit of Earth around the Sun.
Loeb assessed Earth’s ideal situation by saying, “we inhabit a platform from which we can escape easily into interstellar space. . . . This miracle allowed our civilization to design missions, such as Voyager 1 and 2 or New Horizons, that will escape from the solar system.”3
A Just-Right Solar System for Exploration
We have come to take for granted remarkable interplanetary spacecraft, spaced-based global communications, and Earth monitoring. However, some of those achievements would not have been possible were it not for special features of our planet, Sun, and solar system. Here are some examples.
- Geosynchronous orbits: Satellites that have an orbital period that matches the rotation period of the Earth, 24 hours, are said to be geosynchronous. Each day most people on Earth inadvertently make use of satellites in these orbits. Almost a whole hemisphere is constantly visible to a satellite in these orbits, which is useful for global communications and Earth monitoring.
Scientists have shown that habitable conditions on a planet similar to Earth are dependent on a proper rotation rate of the planet—one that’s just-right for the planet’s atmosphere, oceans, continents, and energy flux from its sun.4 If the rotation is appreciably faster than Earth’s, the equator-to-pole temperature differences will be large, resulting in a less suitable global climate. A rotation equal to or slower than Earth’s will result in a more globally uniform climate. However, with a slower rotation rate than Earth’s, a geosynchronous satellite would be much farther from the planet, resulting in less efficient communications, less resolution for planet monitoring, and much more expensive satellites.
It is not necessarily surprising that we find ourselves living on a planet with a rotation rate that supports a suitable global climate. After all, we are here. However, it is surprising that its rotation rate is also suitable for efficient global communications and Earth monitoring.
Figure 1: NOAA’s GOES-16 Satellite Sends First Images to Earth (2017.) Image Credit: NASA
- Sun-synchronous orbits: If a planet’s diameter at the equator is appreciably larger than at its poles (equatorial bulge), a reconnaissance satellite can be put into an orbit such that the satellite crosses a point on the planet at the same solar time each day. The result is that the lighting conditions on the ground are the same for each daily pass of the satellite, a very important requirement for Earth observation. Earth has the just-right bulge to make sun-synchronous orbits a valuable tool for these missions.
Figure 2: Typical Sun-Synchronous Orbit. Image Credit: NASA
- Planet spacing in our solar system: Missions to the innermost planet, Mercury, and to the outer planets would require bigger rockets and longer travel times were it not for “swing bys” of sister planets that can be used to boost the spacecraft by the method of gravity assist. For example, the New Horizons spacecraft swung by Jupiter (2007) on its way to Pluto, shortening its trip to Pluto by three years.
Figure 3: Typical Gravity Assist Trajectory. Image Credit: NASA
- “Grand Tour” of the four outer planets: The Voyager 2 mission (launched in 1977) was designed to take advantage of a rare geometrical arrangement of the outer planets that occurred in the late 1970s. This layout of Jupiter, Saturn, Uranus, and Neptune, which occurs about every 175 years, allowed Voyager 2 to swing from one planet to the next without the need for a large onboard propulsion system. Just at the point in human history when scientists had accumulated the rocket, communications, and instrumentation capabilities required for this type of mission, the planets were in a rare configuration for it to be accomplished. Voyager 2 has since traveled out of the solar system and is still sending valuable data from interstellar space.5
Figure 4: The Grand Tour of Voyager 2 to Jupiter, Saturn, Uranus and Neptune. Image Credit: NASA
With the Command Came the Resources
When God told humans to “fill the earth and subdue it,” that was not just a command. It was also a prophecy that we see being realized today, and we see evidence that God gave humanity ample means to do it. In this way we can view these achievements in space as additional evidence of the accuracy and authority of the Bible.
- Michael Hippke, “Spaceflight from Super-Earths Is Difficult,” International Journal of Astrobiology 18, no. 5 (October 2019): 393–95, doi:1017/S1473550418000198.
- Manasvi Lingam and Abraham Loeb, “Limitations of Chemical Propulsion for Interstellar Escape from Habitable Zones around Low-mass Stars,” Research Notes of the AAS 2, no. 3 (August 30, 2018): doi:10.3847/2515-5172/aadcf4.
- Abraham Loeb, “Escape from Proxima b,” Scientific American Blog Network, April 16, 2018, https://blogs.scientificamerican.com/observations/escape-from-proxima-b/.
- Tiffany Jansen et al., “Climates of Warm Earth-like Planets. II. Rotational ‘Goldilocks’ Zones for Fractional Habitability and Silicate Weathering,” The Astrophysical Journal 875, no. 2 (April 17, 2019): doi:10.3847/1538-4357/ab113d.
- In retrospect, if the Grand Tour opportunity had occurred 40+ years later (today, for example) the mission would yield much more science because of better technology. However, at the time (1970s) the prospect of a forthcoming Grand Tour generated much excitement. It is my opinion that the early success of this mission was an impetus to further exploration of the solar system and beyond.