A major milestone for exoplanets
The number of known planets outside our solar system has exceeded 6,000, according to a tally kept by NASA.
This achievement comes just 33 years after the first exoplanet was observed in 1992.
Josh Colwell and Addie Dove, planetary scientists at the University of Central Florida and hosts of the podcast Walkabout the Galaxy, explained that there are several different ways of identifying exoplanets.
Most have been discovered as the planet transits, or crosses in front of, the star it’s orbiting. Another technique is called radial velocity, by which a shift in the color of a star’s light is observed due to an orbiting planet.
“So, we have to be able to be looking at a really, really bright star, and say, ‘Oh, the lights changed a teeny tiny bit.’ So, we need really great telescopes. We need really good processing techniques. We need to know and understand, sort of what the period is like, how long it would take to make those things. And also, for a lot of these, you need several observations,” Dove said.
Only 20 have been discovered by directly imaging, with less than 100 exoplanets being photographed at all.
In addition to these first 6,000 confirmed exoplanets, there are more than 8,000 candidates that await further observation, according to NASA.
All shapes and sizes of exoplanet have been recorded, many of which are similar to our solar system’s Neptune. Second most common are gas-giants and “Super Earths,” which are larger than Earth but lighter than other gas giants. Some of the planets have shown promise for human habitability.
“The habitable zone is typically defined as where the temperatures could support liquid water on the surface. And we have seen planets in habitable zones. They don't look like Earth in terms of their size and their density, and they're typically orbiting cooler stars, so they're much closer to the star. Sometimes, this gives you a planet that is tidally locked, just like the moon is,” Colwell said.
Who cares about space junk?
Space junk, also known as space debris or orbital debris, is the collection of human-made objects in Earth’s orbit that have been discarded and no longer function.
Occasionally, the debris falls back toward Earth and most of it is burned up in the atmosphere. Pieces that are not burned up typically land in the ocean or in uninhabited areas. In rare cases, large pieces falling towards Earth could pose a risk to humans.
In orbit, space junk can reach speeds of 18,000 miles per hour. According to Patrice Kohl, assistant professor at SUNY College of Environmental Sciences and Forestry, debris could stick around for decades, centuries or even thousands of years.
“As more and more debris accumulates in orbit, the higher and higher risk you have of debris collisions — both with active satellites and spacecraft, and also between two pieces of orbital debris,” Kohl said. “That's really problematic, because you might think when these pieces of debris break up, that they're smaller and they're less dangerous, but the opposite is actually true. Then you basically have a big cloud of shrapnel. This stuff is moving so fast that something the size of a marble can have the impact of a hand grenade.”
Kohl’s research found that American’s concern about space junk isn’t self-centered. 35% of participants said they were extremely or very concerned about the consequences of space junk for space exploration, but just 19% responded the same about consequences for people on Earth.
“One of the things we heard from people in the in-depth interviews is that people didn't really see it as being personally salient. They would say things like, ‘it doesn't really impact me at all in my daily life. I'm not rocketing into orbit, so I'm not too concerned about orbital debris,’” Kohl said.
Governments and commercial space companies have yet to take large steps in clearing space debris, despite concern from scientists. Kohl suggested the inaction was due to a lack of public pressure.
“Stories about, a piece of space junk crashing into a house in Naples, Florida. Flights being grounded or rerouted, because [of] Starship or some other spacecraft has exploded. I think those kinds of stories may be what starts to move the needle in terms of, you know, grabbing people's attention and generating public concern about the issue, and finally, putting public pressure on politicians to fill in gaps in policy,” Kohl said.
Editor's note: Host Brendan Byrne worked previously as a graduate student with Kohl.
