An image of Proxima Centauri taken by the Hubble Space Telescope (Wikipedia)
The closest star to our solar system is one named Proxima Centauri. Proxima Centauri is a relatively small star, as it is a red dwarf star with about 12.5% the mass of the Sun and only about 0.17% as bright as the Sun. Proxima Centauri resides about 4.25 light years away from Earth, and is part of a three-star system with Alpha Centauri A and Alpha Centauri B. A fun fact about Proxima Centauri is that it is a flare star, meaning it changes in brightness every once in a while due to activity of its magnetic field. In 2016, for example, it became 68 times brighter than normal because of a “super flare.” Proxima Centauri also has three known planets orbiting the star, one of which might be a super-Earth residing in the habitable zone of the star where liquid water can exist on the planet’s surface under normal temperature and pressure.
One of Cassini’s most famous images of Saturn (NASA)
The story of the Cassini spacecraft is one of scientific discovery and self sacrifice. Cassini was launched in 1997 and spent 20 years in space, focusing on the planet Saturn, its moons, and its rings, before the spacecraft’s intentional demise in 2017. Through Cassini, we were able to land a probe on Titan, Saturn’s largest moon, and discover seven new moons of Saturn. Cassini also made several flybys of and gained valuable insight into Enceladus, a moon which has a massive subglacial ocean and which has been labeled as one of the most likely places of extraterrestrial life in the solar system. In 2017, Cassini’s “grand finale” was one that both advanced scientific research on Saturn and preserved scientific principles. The spacecraft performed several close flybys of the planet’s rings before finally plunging itself into the atmosphere of Saturn, sending images and data back to Earth up until it burned up in the atmosphere, concluding its scientific mission. This was done in order to prevent any microbes that hitchhiked on the spacecraft from Earth from contaminating Saturn’s moons if it accidentally crashed into one after running out of fuel.
Cassini’s final image before burning up in Saturn’s Atmosphere (NASA)
Over the decades, there have been many hypotheses made about how our Moon was formed. There are many possibilities that we can rule out simply due to the facts that we know about the Universe. Firstly, we know that the Moon was not captured by the Earth’s gravity because the Earth is too small to have enough force to catch such a large celestial body. We also know that the Earth and the Moon could not have formed at the same time because if they had then they would have formed to be roughly the same in composition and density. The leading theory that scientists have devised is that the Moon was formed by the aftermath of another planet colliding with the Earth. This is called the “Giant Impact Hypothesis.” This collision sent particles careening away from the Earth, which began to orbit and eventually collided together to form the Moon that we know today. Another idea that supports this is that a large collision might also be the reason for the Earth’s tilted axis.
A Helpful Visual of the Impact Hypothesis
This theory has a lot of substantial evidence to support it. It is completely plausible that another planet, which would have probably been roughly the size of Mars, could have hit the Earth with enough force to send a large portion of the Earth’s outer shell into space in large pieces of debris. That debris would not have gotten far before it was ultimately restrained by the force of the Earth’s gravity, so it would have formed a ring around the planet. The debris caught in that ring would have slowly collided together over the span of several orbits. Eventually, it would have formed a spherical object and remained in that orbit. This is what astronomers believe to have happened to form the Moon, but there is unfortunately no way to be absolutely certain of it, which is why it remains a theory.
A short video can also be found here to help you to better visualize what this collision and formation would look like.
A new study by Nature Astronomy has tapped an estimate for the greenhouse gas emissions of the astronomy industry. Unfortunately, despite the fact that the global astronomy industry is much smaller than many other industries, its emissions are strikingly large. The number estimated by this study is a staggering 20 million tonnes of CO2 annually. Putting this into context, astronomical researcher Jürgen Knödlseder of France’s IRAP notes in an interview with NPR that this level is on par with the annual emissions of Croatia, Bulgaria or Estonia’s national emissions over a full calendar year. While it is important to note that there is a tremendously long list of industries which pollute more heavily, the astronomy industry should feel a need to correct this because they have large per-capita emissions and, more importantly, it is an important authority on reporting on climate change. For an industry tasked with communicating the urgency of Climate Change to the citizens of Earth, large levels of greenhouse gas emissions may strike the public as hypocritical. Some astronomers have even proposed slowing down the production of new telescopes until the processes become more efficient, or at the very least become primarily powered by renewable energy sources. While not all in the industry will feel comfortable making such a dramatic move, this study should stress to those that love looking out from Earth that we have an urgent, time-sensitive problem right here at home.
While stars are powered by nuclear fusion, nuclear reactors here on Earth have yet to make that leap. Fission is our only readily available source of nuclear power, but it is significantly less lucrative than its counterpart. The difference is the process, which combines two isotopes of hydrogen to trigger an energy release instead of splitting atoms, like in fusion. However, this process requires massive pressure (like in the cores of stars) that is hard to replicate on Earth. To make up for it, advanced facilities like the JET Laboratory use ridiculously hot plasma suspended in a magnetic field, the temperature of which is roughly ten times that of the cores of stars. This excessive heat allows for the process to take place and has been proven to work on small scales. A snapshot of one of these reactions is included below.
At this scale, fusion does not produce a remarkable amount of energy, but it shows more ambitious products have merit. This test in particular, which happened in early 2022, was used as a benchmark to justify support for a ITER, a facility under construction meant to be the next step in fusion exploration.
New findings by the AKARI space telescope, coupled with surface modeling at the Earth-Life Science Institute (ELSI) at Tokyo Institute of Technology present new evidence that the asteroid matter which composes Earth was located much further out in the solar system than initially thought. Their study involved computer modeling to develop reflective spectra of hypothetical materials believed to exist in the primitive outer belt of the solar system. The researchers placed heavy evidence on studying ammonia-bearing clays found on Earth. According to the researchers at Tokyo Institute of Technology, this is interesting because this material can only stabilize and form in conditions that are water-rich and at a very low temperature, akin the the conditions found in the outermost asteroid belts of our solar system. Thus, these researchers propose that the various mineral materials which now compose earth formed in outer orbits of our current solar system, before the mixture was brought closer to the center of the solar system, by mixing processes. Their theory will be tested when their spacecraft, Hayabusa 2, returns samples: if the samples contain ammoniated salts and minerals, it will be strong evidence to put our cosmic history in perspective according to this theory.
If you have participated in observing for class, then you have seen through a telescope the Orion Nebula. Nebulae are star-forming regions that when studied can tell us lots about how stars and solar systems come to be, and the Orion Nebula is no different. When we look at the Orion Nebula through a telescope, four bright stars called the Trapezium are visible. These are relatively young stars that have been formed from the gravitational collapse of dust and gas within the nebula and are very massive at 15-30 times the mass of our sun. However, these are just a small fraction of the stars being formed in the nebula: the nebula is truly massive in scale.
In addition to observing star formation, images of planet-forming regions around stars have been captured in the Orion Nebula. Images such as those shown below help scientists understand how our own solar system was born and to continue to test theories of planet formation.
Protoplanetary disks located inside the Orion Nebula where planetary formation is likely occurring
The Martian originated as a book written by Andy Weir, then was adapted into a movie which was directed by Ridley Scott. The book and the movie prided themselves on being scientifically accurate. In fact, when Andy Weir was first writing the book, he published chapters on his blog, and adjusted them based on the feedback of scientists reading them.
In fairness to the writers, many of the events in the movie, like the gravity assist around Earth and Mars, or Mark being able to survive a brief, partial depressurization of his helmet are all scientifically valid; however, the science breaks down as soon you start looking into the variation of the atmospheric pressure on the planet.
The storm that sparks the initial conflict of the story, while necessary to the plot, is actually impossible in Mars’s thin atmosphere. In fact, the strongest Martian winds amount to a light breeze. Definitely not something strong enough to tip over a spaceship. What’s more, if the Martian atmosphere really was thick enough to cause the damage seen by the storm, then the entire ship modifications used to make Watney’s ascent vehicle would be impossible due to the increased drag it would feel.
Also, Mars has about one tenth the mass of Earth, and therefore gravity is far less on the red planet; however, Watney is rarely shown moving as such in the movie.
Even with these exceptions, both the book and its film adaptation have been praised for their commitment to scientific accuracy. (Wikipedia)
On a personal note, The Martian and its explanation of the scientific concepts behind the story is the main reason that I fell in love with outer space and am pursuing a mechanical engineering degree.
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In discussing how planets and stars form, one will quickly find the nebular hypothesis — an idea that stars and the planets that orbit them were formed from clouds of gas called nebulae. But how was this nebula first formed, where did it come from, and what are the different types of nebulae?
A nebula is simply a cloud of gas with a density of about 100 too 10,000 atoms per cubic centimeter. In comparison, the Earth’s atmosphere has about 2.5×1019 atoms per cubic centimeter (at surface level). Most are composed of hydrogen and sometimes emit a reddish spectrum, but other elements such as oxygen have also been seen (oxygen emits a greenish-blue color depending on temperature).
Nebulae appear from the collapse of stars, or if an extensive amount of time is given, nebulae can form from the clouds of ‘space dust’ that clump together. In the former, not all stars form nebulae in the same way:
Object formed vs. Stellar mass. Depending on the mass of the star collapsing, it can form a variety of stellar remnants.
For a star ranging from about 100 to 250 solar masses, it may be subject to Pair Instability, a phenomena in which electrons and positrons are produced, giving way to the gravitational collapse of the star. If such an event occurs, neither a black hole nor neutron star will be formed, instead, the star will obliterate itself completely, leaving a large nebula behind.
For a nebula to form from cold gas, an immense amount of time is required. These ‘space clouds’ will travel throughout the universe, subject to the gravitational pull of nearby objects, which will sometimes alter the nebula just enough to begin star formation if enough matter has accumulated.
On October 15th, 1997, the rocket carrying the Cassini Spacecraft and its Huygens probe took off from Cape Canaveral. It was sent to the outer solar system to study Saturn, as well as its moons. The Huygens probe was deployed to one of these moons, Titan, recording images and data. In 2017, after running out of fuel 20 years after deployment, the spacecraft was sent into Saturn’s atmosphere to prevent disturbing its moons. Below are some of the images captured by Cassini in its lifetime.
In this picture captured by Cassini in the second half of its mission, Enceladus, a notable moon is in the foreground with Pandora, a smaller moon, in the background.
This image captures Enceladus more than a year later, clearly showing fractures on its surface. Additionally, this picture shows the jets emitted from the surface of the moon.
