In class, we have discussed the possibility that life on Earth did not originate on Earth, but came to Earth on an asteroid or other impactor. But another idea is that the inverse is true: Later impacts on Earth sent life to other locations in the Solar System. Recent simulations suggest that some of the known or believed impacts Earth has sustained were large enough to send some debris to Mars, Jupiter, and possibly even Saturn. We know that Mars may have once been habitable, and we suspect that one or more of Jupiter’s moons are habitable—so is it possible that some extremophiles, such as waterbears, were included in the debris that got sent to other worlds and started life there? Some scientists think so.
In using the Drake equation to discuss and estimate the probability of non-Earth life in our universe, one factor we estimated was the probability of life developing on a given planet in the habitable zone. The problem with making such an estimate as students in an Astronomy 201 course, of course, is that we all know next to nothing about how life comes to be, even when all of the right chemicals are present.
The thing is, nobody knows exactly how abiogenesis happens. But scientists who study it naturally have a lot of ideas. We learned in class about the Miller-Urey experiment, in which organic compounds were made from common atmospheric compounds and energy. While there is no standard model for the beginning of life, most leading models draw from the same ideas that Miller and Urey did, and rely on the results from their experiment and similar experiments.
But without a truly accepted model of abiogenesis, it is difficult to predict what fraction of habitable planets develop life, and to me this is the weakest part of our Drake equation. If any part of the equation is guesswork, then the result is just guesswork—and there is nothing concrete about our guesses on the probability of the development of life.
In learning about the interiors, we’ve heard a lot about metallic hydrogen. To me, it was a confusing idea, simply because I only really hear about hydrogen in the context of being a gas or being a compound such as water or methane. Furthermore, it was not clear what phase metallic hydrogen would be, since usually “metallic” is not actually a phase, just a set of properties.
Dr. Grundstrom told us that the main thing we need to know about metallic hydrogen is that it is conductive, and in fact this is the primary characteristic in its definition. As it turns out, metallic hydrogen has never been created experimentally on Earth, because it requires more pressure than we currently know how to create. However, it is theorized that metallic hydrogen takes a liquid form, rather than the solid one might expect at such pressures. As we discussed in class, several celestial bodies—most notably, Jupiter and Saturn—are believed to be full of liquid metallic hydrogen, thanks to the huge amount of gravity produced by the mass of those objects.
Ever since the IAU gathered in Prague in 2006 and published a new scientific definition of “planet”, there has been debate on how well they did, and whether they were right to “demote” Pluto from planet to the new “dwarf planet” classification. I aim here to critique the IAU’s definition of a planet.
First, here is the final definition the IAU came up with:
The IAU therefore resolves that planets and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way:
(1) A “planet”¹ is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
(2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape², (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
(3) All other objects³, except satellites, orbiting the Sun shall be referred to collectively as “Small Solar-System Bodies”.
¹ The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
² An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
³ These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.
Here’s my take on what they published, point-by-point:
- Right off the bat, the IAU is restricting the definition to objects “in our Solar System”. On the one hand, this caveat is good: it makes sure to not preclude extrasolar objects from being considered planets. That is, if you discovered one of the over 5000 other known planets in the universe, nothing here is suggesting that you can’t call it a planet. On the other hand, nothing here says you can call it a planet either. All of these other objects are explicitly not defined here. Shouldn’t a brand-new definition of “planet” in this age of extrasolar discovery make sure to actually define the word for all—or at least most!—possible scientific uses? I think it should, and thus find the very premise of this definition lacking.
- A planet or a dwarf planet must be a “celestial body”. Technically, “celestial” means an object in the sky outside of Earth’s atmosphere, precluding Earth from being a planet. This technicality is ignored in practice, but it is still a mistake that should not be in the definition.
- A planet and dwarf planet must orbit the Sun. Since the definition only covers the Solar System already, this is fine. But it would be easy enough to replace “the Sun” with “a star or star system” here for a broader definition.
- A planet and dwarf planet must have enough gravity to be basically a sphere. This seems to be an agreeable requirement, and is well-defined within the broader definition.
- A planet “has cleared the neighbourhood around its orbit”, while a dwarf planet “has not the cleared the neighbourhood around its orbit”. This is the primary distinction between planet and dwarf planet—and its meaning is not at all clear! The read of this definition is given no clues as to what a large space object’s “neighborhood” is, let alone what it would mean to “clear” such a neighborhood. In my opinion, it is completely unacceptable to publish a definition, meant primarily to create a distinction between Pluto and the other original planets, wherein this primary distinction is itself undefined. As the saying goes, “YOU HAD ONE JOB.” In practice, it seems that “cleared the neighbourhood” is interpreted as meaning that any of the object’s moons have their orbital center of mass within the object itself. Thus, Pluto is a “dwarf planet” rather than a “planet”, because the center of mass between Pluto and it’s “moon”, Charon, is between the two objects, rather than inside Pluto. But official definition should lead to the practice; not be left open to a broad interpretation, and it is still not clear to me why other dwarf planets, such as Eres, are not considered to have cleared their neighbourhood.
- A dwarf planet cannot be a “satellite”. This just means it can’t be orbiting another planet or dwarf planet or moon or whatever, because a moon would still technically fit the “in orbit around the Sun” requirement (by way of orbiting another body that orbits the Sun). It is not clear why the definition for “planet” does not need this rule, which ultimately leads back to the ambiguity of “cleared its neighbourhood”.
- Everything else is a “Small Solar-System Body”. OK, I’m not sure what the capital letters are for, and it’s a pretty pedantic name, but this is fine I guess.
Overall, I find the definition lacking, particularly in its prime objective of defining exactly why Pluto et al. are not strictly planets (but they are still dwarf planets, which is apparently not just a regular planet with a modifier before it). It makes sense that the IAU didn’t want to open the door to adding potentially dozens of new planets to our Solar System, but it doesn’t make sense that they couldn’t write the official definition in a more robust manner.
Despite popular, largely politically-based claims to the contrary, global warming is a scientific observation explained by an accepted, well-defined scientific theory. Most debate over whether global warming exists and how it is caused occurs not among scientists who study climate change, but among the general public, mostly due to a lack of understanding and what is called the politicization of science.
Lobbyists for corporations and other entities often twist, cherry-pick, and/or simply lie about scientific studies for the purpose of achieving their own political or ideological ends—often, turning a profit. Since politicians (who listen to the lobbying) regularly interact with the public, but the scientists who have actually studied the subject in great detail usually don’t, the politicized science is what the general public hears far more often. And, because different lobbies twist science in different ways, conflicting “facts” become common beliefs, and the debate is generated.
While those who know the most about global warming (climate change scientists) have moved past any doubts about the existence and general causes of global warming, national policies are shaped by a public opinion informed by a varying mix of some actual science and a lot of conflicting politicized science. And for this, the process of saving the climate that we know how to survive in is slowed drastically.
Someone named Josh Worth made a to-scale model of our solar system wherein the Moon is only one pixel in diameter, and it’s totally awesome. The horizontally-scrollable webpage starts at the Sun, and moves right, with text interspersed into the vast distance between planets. What’s so cool about this particular model is that it represents both distance and size to the same scale, something that I have seen very few, if any, models do before.
We talked pretty extensively about the scale of the universe early on in the semester, but it’s something else entirely to really experience that scale to some degree. Worth’s text between planets is poignant at times, discussing the significance of human life to the universe. I would guess it took me about 20 minutes to scroll and read from the Sun to Pluto, and I strongly recommend you do so too.
The Space Race was a competition of sorts between the United States and the Soviet Union that started in 1955 and led to the first artificial satellites being sent into orbit, the first humans being sent into space, and the first humans landing on the Moon. The USA was the first to announce intentions to create a satellite, and the race began when the USSR made a similar announcement just four days later, on August 2, 1955. The two large countries were already in an arms race thanks to their simultaneous discovery of German missile technology at the end of World War II, and there is no doubt that the sense of rivalry stemming from that fact contributed to both the Space Race and the Cold War.
As it happened, the USSR launched its satellite, Sputnik 1, first. They also were the first to successfully send humans into space, meaning all of the pressure was on the USA to get to the moon first. This was accomplished in 1969 with the Apollo 11 mission, and after that the Space Race (along with the Cold War) slowly fizzled out.