Throughout this article series, I’ve highlighted major events that took place during our solar system’s youth and helped pave the way for the eventual appearance of humanity. In part 1, I described the solar system’s birthing experience. Part 2 outlined the 50 million years of fine-tuning following the solar system’s birth, particularly (1) the configuration of the gas giant planets and (2) the collision event that formed the Moon. In part 3, I began describing other fine-tuned events that took place during the next 800 million years of the solar system’s history, specifically the Sun’s instability and the migration of Jupiter and Saturn into their present orbits.
This week, I will pick up where I left off in part 3 and discuss a turbulent time in Earth’s history known as the Late Heavy Bombardment (LHB), a relatively brief episode that occurred 700 million years after the solar system planets formed, during which hundreds of thousands of asteroids and comets bombarded Mars, Earth, the Moon, Venus, and Mercury. In 2005, a team of four planetary scientists published a total of four papers describing a possible 1:2 orbital resonance event between Jupiter and Saturn (see part 3). In their third paper, the team showed that this event also yielded the long-sought answer to the cause of the LHB.1
Origin of the Cataclysmic Late Heavy Bombardment
Radiometricly dated ages of impact melt rocks collected during Apollo missions 15, 16, and 17 provided the first evidence for the LHB. These measurements produced dates that clustered between 3.8 and 4.0 billion years ago. Subsequently, astronomers measured the erosion patterns on the Moon craters. (The Moon possesses a very thin atmosphere of mostly argon gas that erodes its craters slightly over the course of a few billion years.) These erosion patterns demonstrated that over 90 percent of the Moon’s craters formed about 3.9 billion years ago.
Subsequent to that discovery, astronomers measured the erosion patterns of both Mercury’s (see figure 1) and Mars’ craters. These measurements and others confirmed that the entire inner solar system suffered a cataclysmic bombardment of asteroids and comets that spanned no more than a hundred million years between 3.95 and 3.80 billion years ago and peaked between 3.90 and 3.85 billion years ago.2
Figure 1: Craters on Mercury
Almost all the craters seen in this image show a slight degree of erosion generated by Mercury’s thin atmosphere. The erosion measurements establish that virtually all of the cratering events occurred between 4.0 and 3.8 billion years ago.
Image credit: NASA
In their third paper, the planetary science research team showed that when the 1:2 orbital resonance between Jupiter and Saturn occurred it destabilized the orbits of Uranus and Neptune. This, in turn, disrupted the huge cloud of planetesimals, asteroids, and comets orbiting in the vicinity of the four gas giants, triggering a sudden delivery of hundreds of thousands of projectiles into the inner solar system. The team also established that the disruption strongly perturbed the asteroid belt between Jupiter and Mars. The combined effect perfectly explains the LHB.
In a fourth paper, the team determined that the 1:2 orbital resonance event [explains all the observed features of the Kuiper Belt, as well as Neptune’s orbit.3 The Kuiper Belt (see figure 2) is a region of the solar system that extends from the orbit of Neptune at 3 billion miles from the Sun out to slightly more than 5 billion miles from the Sun. In this zone astronomers have discovered, in addition to Pluto, three dwarf planets or plutoids—Eris, Haumea, and Makemake—and over a thousand asteroids and comets. What they have found so far causes them to conclude that at least 70,000 bodies bigger than 100 kilometers (62 miles) in diameter must exist in the Kuiper Belt. Astronomers estimate that the total mass of Kuiper Belt objects is about one hundred times greater than the total mass of the Main Belt asteroids that reside between the orbits of Mars and Jupiter.
Figure 2: The Kuiper Belt and Jupiter’s Trojan Asteroids (as of 2007)
There is a main population of Kuiper Belt objects (green) and a scattered population (orange). The two pink zones emanating from Jupiter represent the Trojan asteroids.
Data credit: The Minor Planet Center; image credit: drink beer!
Specifically, the planetary scientists showed that the solar system’s primordial disk of planetesimals—initially centered roughly on Saturn’s orbit—must have been truncated at roughly 3 billion miles outward from the Sun. This truncation would explain the sudden halt in Neptune’s outward migration and the position of its present orbit. This means that the Kuiper Belt was empty initially. However, the 1:2 orbital resonance event between Jupiter and Saturn thrust what remained of the huge cloud of planetesimals, asteroids, and comets outward to between the orbits of Uranus and Neptune. That event also excited the eccentricity of Neptune’s orbit to a value as high as 0.3 (eccentricity of a circle = 0, of a parabola = 1, of an ellipse = greater than 0 but less than 1). Interaction between the cloud and Neptune with its high eccentricity orbit explains eight present-day characteristics of the outer solar system:
- The distance of Neptune’s orbit from the Sun
- The extremely low eccentricity of Neptune’s orbit
- The coexistence of both a resonant and non-resonant population of Kuiper Belt objects
- The eccentricity inclination distribution of the plutoids and plutinos
- The outer edge of the Kuiper Belt at the 1:2 mean motion resonance with Neptune
- The correlations between inclination and physical properties of classical Kuiper Belt objects
- The existence of an extended scattered disk within the Kuiper Belt
- The bimodal inclination distribution of classical Kuiper Belt objects
The team definitively established that the present-day Kuiper Belt is the leftover remnant of the enormous cloud of planetesimals, asteroids, and comets that originally centered roughly on Saturn’s orbit.4 The fact that the Kuiper Belt, as large and as massive as it is, is only about 1 percent the size of the original cloud testifies to the catastrophic nature of the Jupiter-Saturn resonance event.
Over the course of six years, the planetary science research team has established a remarkable breadth of solar system features explained by the 1:2 orbital resonance event between Jupiter and Saturn. Other groups have added to the list of features explained by the event:
- characteristics of Saturn’s rings and moons,5
- the elimination of the E-Belt of asteroids6 (part of the primordial Main Belt that orbited close to Mars’ orbit),
- the heavy element enrichment of the gas giants’atmospheres,7
- contamination of the Main Belt by primordial trans-Neptunian objects,8
- the orbital characteristics of the Eos family of asteroids,9 and
- the elevated abundances of highly siderophile (iron-loving) elements (rhenium, osmium, iridium, ruthenium, platinum, and palladium) in the mantles of Earth, Mars, and the Moon.10
But the LHB did more to Earth than just load it up with highly siderophile elements. It altered the tilt of the planet’s rotation axis by as much as 10 degrees.11 It infused Earth’s core with extra sulfur, oxygen, iron, uranium, and thorium12 and removed much of Earth’s chlorine and other halogens.13 It also reconfigured the planet’s atmosphere, crust, mantle, outer core, and inner core.
The details of the 1:2 orbital resonance event and the LHB play a significant role in making possible the existence of advanced life on Earth. Next week, I will explain how these design details, plus a newly discovered feature, help establish that a supernatural, super-intelligent Creator was intimately involved in ensuring that the solar system and Earth, in particular, had the just-right “childhood” history to prepare them for sustaining human beings.
1. R. Gomes et al., “Origin of the Cataclysmic Late Heavy Bombardment Period of the Terrestrial Planets,” Nature 435 (May 26, 2005): 466–69.
2. Hervé Martin et al., “4. Building a Habitable Planet,” Earth, Moon, and Planets 98 (June 2006): 97–151, DOI: 10.1007/s11038-006-9088-4.
3. Harold F. Levison et al., “Origin of the Structure of the Kuiper Belt during a Dynamical Instability in the Orbits of Uranus and Neptune,” Icarus 196 (July 2008): 258–73.
4. Alessandro Morbidelli et al., “Origin of the Structure of the Kuiper Belt during a Giant Planets Orbital Instability,” Bulletin of the American Astronomical Society 38 (September 2006): 583; Alessandro Morbidelli et al., “Chaotic Capture of Planetesimals into Regular Regions of the Solar System. I. The Kuiper Belt,” American Astronomical Society, DDA Meeting #39 (May 2008): abstract #12.04.
5. Sébastien Charnoz et al., “Did Saturn’s Rings Form during the Late Heavy Bombardment?” Icarus 199 (February 2009): 413–28.
6. W. F. Bottke et al., “The E-Belt: A Possible Missing Link in the Late Heavy Bombardment,” 41st Lunar and Planetary Science Conference, held March 1–5, 2010 in The Woodlands, Texas. LPI Contribution No. 1533: 1269.
7. A. Matter, T. Guillot and A. Morbidelli, “Calculation of the Enrichment of the Giant Planet Envelopes during the ‘Late Heavy Bombardment,’” Planetary and Space Science 57 (June 2009): 816–21.
8. Harold F. Levison et al., “Contamination of the Asteroid Belt by Primordial Trans-Neptunian Objects,” Nature 460 (July 2009): 364–66.
9. Alessandro Morbidelli et al., “Are Some Asteroid Families from the Time of the Late Heavy Bombardment?” Bulletin of the American Astronomical Society 42 (October 2010): 949.
10. William F. Bottke et al., “Stochastic Late Accretion to Earth, the Moon, and Mars,” Science 330 (December 10, 2010): 1527–30.
12. B. J. Wood and M. R. Kilburn , “Metal-Silicate Partitioning and the Incompatibility of S and Si During Core Formation,” Earth and Planetary Science Letters 152 (November 1997): 139–48; Gerlind Dreibus and Herbert Palme, “Cosmochemical Constraints on the Sulfur Content in the Earth’s Core,” Geochimica et Cosmochimica Acta 60 (April 1996): 1125–30; Fabrice Gaillard and Bruno Scaillet, “The Sulfur Content of Volcanic Gases on Mars,” Earth and Planetary Science Letters 279 (March 15, 2009): 34–43; G. Fiquet, J. Badro, and F. Guyot, “New Constraints on Earth’s Core Chemical Composition,” American Geophysical Union, Fall Meeting 2004, (December 2004): abstract #MR41A-01; Doris Breuer, Stephane Labrosse, and Tilman Spohn, “Thermal Evolution and Magnetic Field Generation in Terrestrial Planets and Satellites,” Space Science Reviews 152 (May 2010): 449–500; David Gubbins et al., “Gross Thermodynamics of Two-Component Core Convection,” Geophysical Journal International 157 (June 2004): 1407–14; G. F. Davies, “Geophysically Constrained Mantle Mass Flows and the 40Ar Budget: A Degassed Lower Mantle?” Earth and Planetary Science Letters 166 (March 1999): 149–62; Benton Clark, “Death by Sulfur: Consequences of Ubiquitous S Before and After the Biotic Transition, for Mars and Other S-Rich Planets,” Astrobiology 8 (April 2008): 433; David C. Rubie, Christine K. Gessmann, and Daniel J. Frost, “Partitioning of Oxygen During Core Formation on the Earth and Mars,” Nature 429 (May 6, 2004): 58–61; Carl B. Agee, “Earth Science: Hot Metal,” Nature 429 (May 6, 2004): 33–35.
13. Z. D. Sharp and D. S. Draper, “The Chlorine Abundance of Earth: Evidence for Early Atmospheric Loss and Creation of a Life-Supporting Planet,” American Geophysical Union, Fall Meeting 2009(December 2009): abstract #V13H-05.