Can Swift Tuttle have impacted Earth?

This is a simulation of Comet 109P / Swift Tuttle hitting Earth in a Skip Impact. The original orbit's inclination to the Ecliptic would have been 62.7°, and the final / present angle is 66.6°. The Earth's tilt is shown as 22.4° - slightly less than the maximum. The point of impact is aimed at Lake Michigan to show that comet Swift Tuttle could have impacted there and to show that the ejecta would land across the US, potentially forming the Carolina Bays.

The above image is from the CometSkipImpacts program created by John Burgener for this poster. You can download it and try out many different simulations with larger or smaller comets, and different impact orientations. It is available on the web site: www.craters.ca/CometSkipImpacts.exe

This poster is proposing that Lake Michigan is a resultant crater from a skip type impact by comet Swift Tuttle. Comet impacts on Earth are rare, and skip impacts would be only 1% of any impacts that happen. So such an event would be very rare. However, rare is not the same as impossible. It is useful to review how comets and Earth can interact, and what range of impacts can happen.

Skip Impacts are Possible:

Following is an iSALE simulation of a Skip type impact. The comet is larger than realistic to show the effect more clearly.

iSALE is a well recognized hydrocode program able to show impacts with reasonably accurate simulations that match real craters. The above iSALE simulation shows that comets can do low angle skip type impacts and produce effects such as shown in the first video. However, iSALE simulations are less detailed due to limitations of the size of blocks being considered, and due to time. An iSALE run takes weeks. The CometSkipImacts program runs a simulation in minutes and shows higher resolution effects, but is less geologically accurate. It is mainly useful in helping one visualize the possibilities with skip type impacts.

There are many alternative Skip Impacts that can happen. Following are some more examples. These and many other configurations are possible. Direct impacts are also possible. The intent of this poster is not to show all possibilities, but the one that best fits the explanation for the present fireball orbit distribution. Many possibilities exist, but only ONE actually happened. And only two of the following cases can provide the present resultant Swift Tuttle orbit with a 66.55° orbital inclination after the impact: The Swift Tuttle Impact shown above and the comet overtaking Earth. Both also are able to hit Earth at the location of Lake Michigan. It is worth noting that an impact by a comet traveling from the sun or head on will not be able to produce a Lake Michigan location of a skip impact.
 

There are four basic categories of comet impacts with Earth:

1. Catching up from behind Earth with a 10-11 km /sec speed difference.

2. Heading towards or from the Sun, crossing Earth's orbit at a near 90° angle, with a 41 km/sec speed difference.

3. Passing Earth's orbit from an orbit not in the ecliptic plane such as with Swift Tuttle's 66.55° inclination to the Ecliptic plane, with a speed difference of 40 km/sec.

4. Moving in a retrograde path (orbiting around the sun in the opposite direction to most planets, asteroids and comets) and hitting Earth head on, with a 70 km/sec speed difference.

At present, there are comets in all four such categories that have Earth crossing orbits. They are not likely to hit Earth due to the very short period of time in their long orbit paths that bring them close to where Earth could be. Both the comet and Earth need to be at the same spot at the same time. However, low probability is not the same as impossible. Here are images of possible skip impacts from each category, followed by some NASA orbit path images of some of the presently known comets showing the 4 categories. The range of possible impacts is shown here for clarification of the possibilities. The premise of the poster is that a particular comet has previously impacted Earth. The following images and notes are not the proposed impact, but similar ones worth noting as possibilities of other impacts.

Sample Skip Impacts

Skip Impact by comet overtaking Earth. Relative speed of 10 to 11 km/s:

Skip Impact by comet traveling from closer approach to sun and crossing Earth's orbit at aprox. 90°. Relative speed of such an impact is approximately 41 km/s.

Skip Impact by comet traveling in retrograde orbit, hitting head-on, with a relative speed of 70 km/s:

Real Comets with similar orientations as above examples:

Comets typically travel in the Ecliptic Plane, and typically in the same direction as Earth and the planets circle around the Sun. With most comets originating from the Kuiper Belt, this is expected and accepted as the main group of comets. However, as comets interact with the planets, their orbits often get changed and any imaginable orientation is possible. So there are 4 main categories of comet orbits that intersect Earth's orbit:

1. Approaching Earth in a similar plane and direction to Earth's Orbit. The example below is the orbit of C/1991 L3  Levy.  Levy's orbit merges with Earth’s Orbit on the Ecliptic, with both traveling in the same direction as they pass. Levy moves faster than Earth, so an impact would require Levy to approach from behind Earth, and catch up. The original speeds are 41 and 30 km/s, the difference about 11 km/s, but gravity would add to the difference as they approach, so such an impact would be about 12 to 14 km/s. C/1991 L3 Levy is about 11.6 km in diameter.

Comet C/1991 L3 Levy approaching Earth in similar plane and direction to Earth's Orbit - Image from JPL Small-Body Database Browser

2. Crossing Earth's orbit on a closer approach to the Sun. For example, C/1996 B2 (Hyakutake): which crosses Earth’s Orbit on the Ecliptic, but still at right angles to Earth's orbit. Impacts would be at ~ 41 - 43 km/s.

C/1996 B2 (Hyakutake): Crossing Earth’s Orbit  on the Ecliptic

3. Crossing Earth's Orbit from above/below the Ecliptic plane. For example, comet 109P Swift-Tuttle. It is presently inclined at 66.55°. Crossing Earth’s orbit from above the Ecliptic, adding its vector speed to Earths at nearly a right angle, so the impact speeds would be ~ 41 to 43 km/s.

109P Swift-Tuttle: Crossing Earth’s orbit from above the Ecliptic, present inclination of 66.55°.

4. Approaching Earth in a similar plane but opposite direction to Earth's Orbit. The example below is 1P Halley's Comet. It is in a retrograde orbit, passing Earth at ~ 41 km/s, in the opposite direction to Earth's orbit, so impacts would be in the order of 70 km/s.

1P Halley's Comet: Retrograde orbit.

Orbits calculated from ejecta of a Skip Impact

The ejecta / debris from a skip impact by Swift Tuttle will produce the fireball range of orbits observed by NASA. The above image is from the CometSkipImpacts program. After the impact is generated, the orbits can be calculated and plotted to show their orbits after Earth has moved away. With a unique origin at the intersection of Earth and Swift Tuttle, the orbits are all random in size, due to the random nature of the ejecta being tossed with variable energy. But they will retain the point of origin as a common point.

This proposal predicts the wide range of orbits observed, and the unique common point in the orbits.

The abundance of orbits shown in NASA's chart also indicates a relatively recent origin. With time, the fireballs will be swept up and their presence decline dramatically. Comets also break up over time and have limited lifetimes in close orbits to the Sun. The limits on the comet's life time and the debris' lifetimes indicates that the skip impact must have been in the past several thousand years, not millions of years ago.

Ice Falls:

Assuming that Swift Tuttle hit Earth at the end of the ice age, causing the Carolina Bays and the Younger Dryas event, then one should expect that a lot of blocks of ice were tossed into space. Not surprisingly, there are many recorded reports of large ice blocks falling out of the sky. John Saul reports a long list of ice falls in the Meteorite - Quarterly Magazine, 2006. One item in particular is the June 26, 1985, fall of a 1500 pound slab of ice, in Hartford, Connecticut. It is expected if there is a lot of ice debris in space, but not possible as an atmospheric phenomena. For more information on ice falls, there are several web sites on the topic at present such as: tierra.rediris.es/megacryometeors/

A possible objection would be that if the comet did impact Earth as proposed, then there must be many very large pieces of debris. The fireballs are small relative to the amount of debris that would be tossed into space. However, it is apparent that larger pieces would have lower velocity - less velocity for a given amount of energy transfer. As such, most of the larger pieces fell back to Earth shortly after the impact. Some in-between sizes would have been sent out to space, but still would have lower velocities than the smaller pieces, so their orbits would send them much closer to the sun, dramatically shortening their life expectancy.

Comet Swift-Tuttle's fireball orbits can be best explained by an impact origin.

It is proposed that approximately 12,700 years ago, comet Swift Tuttle interacted with Earth. It is proposed that Swift Tuttle at the time was much larger, and that a significant part of it would have been shattered in the impact. If it was originally traveling at an inclination of approx. 63°, after the impact its orbit would change to the present 66.55° inclination.

It is proposed that it hit in the present location of Lake Michigan leaving a long, shallow, scar about 300 km long. The shape of Lake Michigan is close to the shape and size of Mar's Orcus Patera crater. Such craters are possible! Orcus Patera has raised sides from debris tossed sideways – effectively a crater rim. Lake Michigan would have had a 2 to 3 km thick layer of ice on the land at the time of the impact. The crater rim would have been mainly ice, and have melted away over time.

A comet in close approach to Earth is likely to break up due to gravitational stress. It would be expected that the impact would involve more than one piece. The Bathymetric maps of the Great Lakes shows 5 likely elliptical depressions that would fit as 5 spots of impact. Northern Lake Michigan is heavily scared from glaciation, as is most of Lake Superior. But the indicated elliptical areas are free of any glaciation scars, indicating that these areas were not formed by glaciers.

The Carolina Bays line up in a few limited orientations, all of which line up with the proposed impact locations in Lake Michigan and Lake Superior. An impact during the ice age would have 2 to 4 km of ice on the surface. A significant portion of the debris would be ice.

The debris that falls back to Earth from such an impact at the end of the ice age would also cause devastation across North America, and explain the extinction event that killed all of the large mammals in North America. Large ice blocks falling from the sky would kill animals as easily as rocks. The falling rocks would heat on return to the atmosphere, and set fires across North America.

At present, there is no recognized crater to account for a Younger Dryas impact. It is proposed that Lake Michigan is the impact crater related to the Younger Dryas event.