The expected peak of 2023\u2019s\u2019s Geminid meteor shower is around December 13 and 14. This year, a thin waxing crescent moon will be gone long before the peak viewing time (around 2 a.m.) of the meteors. The Geminid\u2019s radiant point rises in mid-evening, so you can start watching earlier at night than most meteor showers! Read more about 2023\u2019s Geminid meteor shower.<\/em><\/p>\n Most meteors in annual showers\u00a0have comets as their sources. But not December\u2019s Geminid meteors, whose source, known as 3200 Phaethon, is a strange hybrid of an asteroid and a comet. This \u201crock-comet\u201d isn\u2019t icy, like a comet is. But it\u2019s known to brighten as it nears the sun, as comets do. And it has a tail. Plus, it spawns the Geminid meteor shower. And so scientists have long puzzled over 3200 Phaethon. How can a rocky asteroid leave behind debris that sparks a meteor shower? Where does its tail come from?<\/p>\n Scientists continue to find answers to how this asteroid can produce one of the year\u2019s best meteor showers.<\/p>\n Available now! 2024 EarthSky lunar calendar. A unique and beautiful poster-sized calendar showing phases of the moon every night of the year. Makes a great gift!<\/p>\n On November 28, 2023, a team at the University of Helsinki released a press release linking a rare type of meteorite to the asteroid 3200 Phaethon. They based their findings on a study published in the journal Nature Astronomy on November 2, 2023. <\/p>\n Researchers at the University of Helsinki compared an infrared spectrum of 3200 Phaethon \u2013 from NASA\u2019s Spitzer space telescope \u2013 to infrared spectra of known meteorites. They found Phaethon\u2019s spectrum showed olivine, carbonates, iron sulfides, and oxide minerals were all present in the asteroid. And that matches the composition of CY carbonaceous chondrite meteorites. These are rare types of meteorites with only six samples available for study.<\/p>\n When they expose CY meteorites to high temperatures \u2013 like those when 3200 Phaethon passes near the sun \u2013 the carbonates in the meteorites produce carbon dioxide, releasing water vapor, and the sulfides release sulfur gas.<\/p>\n While these findings may explain how 3200 Phaethon releases gas near the sun, what about the dust and cometary debris that results in the Geminid meteor shower? <\/p>\n According to their study:<\/p>\n The researchers used experimental data from other studies in conjunction with their thermal models, and, based on them, it was estimated that when the asteroid passes closest to the sun, gas is released from the mineral structure of the asteroid, which can cause the rock to break down. In addition, the pressure produces by carbon dioxide and water vapor is high enough to lift small dust particles from the surface of the asteroid.<\/p>\n<\/blockquote>\n Their lead author, postdoctoral researcher Eric MacLennan from the University of Helsinki said:<\/p>\n Sodium emission can explain the weak tail we observe near the sun, and thermal decomposition can explain how dust and gravel are released from Phaethon.<\/p>\n<\/blockquote>\n And associate professor Mikael Granvik from the University of Helsinki summed it up:<\/p>\n It was great to see how each one of the discovered minerals seemed to fall into place and also explain the behavior of the asteroid.<\/p>\n<\/blockquote>\n Their study also ties in with previous findings released by NASA in 2021. <\/p>\n On August 16, 2021, scientists with NASA\u2019s Jet Propulsion Laboratory in Pasadena, California, announced a possible explanation to 3200 Phaethon\u2019s comet-like behavior. Part of the answer might be\u00a0sodium fizzing from the asteroid\u2019s surface. Their statement explained that this asteroid:<\/p>\n \u2026 brightens as it gets close to the sun. Comets typically behave like this: When they heat up, their icy surfaces vaporize, causing them to become more active and brighten as the venting gases and dust scatter more sunlight. But what is causing Phaethon to brighten if not vaporizing ices?<\/p>\n The culprit could be sodium. As the new study\u2019s authors explain, Phaethon\u2019s elongated, 524-day orbit takes the object well within the orbit of Mercury, during which time the sun heats the asteroid\u2019s surface up to about 1,390 F (750 C). With such a warm orbit, any water, carbon dioxide or carbon monoxide ice near the asteroid\u2019s surface would have baked off long ago. But, at that temperature, sodium may be fizzing from the asteroid\u2019s rock and into space.<\/p>\n<\/blockquote>\n Astronomer Joe Masiero of IPAC at Caltech was lead author of this study. He said:<\/p>\n We know it\u2019s an asteroid and the source of the Geminids. But it contains little to no ice, so we were intrigued by the possibility that sodium, which is relatively plentiful in asteroids, could be the element driving this activity.<\/p>\n<\/blockquote>\n Masiero and his team said observations of Geminid meteors inspired them. Their statement explained:<\/p>\n When meteoroids \u2013 small pieces of rocky debris from space \u2013 streak through Earth\u2019s atmosphere as meteors, they disintegrate. But before they do, friction with the atmosphere causes the air surrounding the meteoroids to reach thousands of degrees, generating light. The color of this light represents the elements they contain. Sodium, for example, creates an orange tinge. The Geminids are known to be low in sodium.<\/p>\n Until now, it was assumed that these small pieces of rock somehow lost their sodium after leaving the asteroid. This new study suggests that the sodium may actually play a key role in ejecting the Geminid meteoroids from Phaethon\u2019s surface.<\/p>\n [We] think that as the asteroid approaches the sun, its sodium heats up and vaporizes. This process would have depleted the surface of sodium long ago, but sodium within the asteroid still heats up, vaporizes, and fizzes into space through cracks and fissures in Phaethon\u2019s outermost crust. These jets would provide enough oomph to eject the rocky debris off its surface. <\/p>\n So the fizzing sodium could explain not only the asteroid\u2019s cometlike brightening, but also how the Geminid meteoroids would be ejected from the asteroid and why they contain little sodium.<\/p>\n<\/blockquote>\n Bj\u00f6rn Davidsson of NASA\u2019s Jet Propulsion Laboratory was a co-author of the study. He added:<\/p>\n Asteroids like Phaethon have very weak gravity, so it doesn\u2019t take a lot of force to kick debris from the surface or dislodge rock from a fracture. Our models suggest that very small quantities of sodium are all that\u2019s needed to do this. It\u2019s nothing explosive, like the erupting vapor from an icy comet\u2019s surface. It\u2019s more of a steady fizz.<\/p>\n<\/blockquote>\n Read more: Fizzing Sodium Could Explain Asteroid Phaethon\u2019s Cometlike Activity<\/p>\n By the way, the comet-like behavior of this asteroid isn\u2019t the only unusual thing about it. For one thing, 3200 Phaethon has an odd color for an asteroid. Most asteroids are dull grey to red, depending on the type of material on their surface. 3200 Phaethon is blue. Blue asteroids are known, but make up only a fraction of all known asteroids. And Phaethon isn\u2019t just blue. It\u2019s one of the bluest<\/em> of similarly colored asteroids (or comets) in the solar system.<\/p>\n Here\u2019s another odd feature of 3200 Phaethon. While comets tend to have more elliptical orbits, asteroid orbits are more circular. 3200 Phaethon\u2019s orbit \u2013 which is now exceedingly well known \u2013 is highly elongated, reminiscent of some comets. Its orbit crosses the orbits of Mars, Earth, Venus and Mercury. <\/p>\n Plus, its orbit brings 3200 Phaethon closer to the sun than any other named asteroid (though some smaller, unnamed asteroids come even closer). At its closest point, Phaethon is only 13 million miles (20.9 million km) from the sun. That\u2019s less than half of Mercury\u2019s closest distance. <\/p>\n The name of this object \u2013 3200 Phaethon \u2013 honors its relationship to the sun. In Greek mythology, Phaethon was the son of the sun god Helios. <\/p>\n 3200 Phaethon is classified as a potentially hazardous asteroid. But that doesn\u2019t mean it\u2019s a threat to Earth. It just means two things. First, 3200 Phaethon is big. The latest estimates (2021) suggest it\u2019s 3.6 miles (5.8 km) wide. It\u2019s big enough to cause significant regional damage if it were<\/em> to strike Earth. Second, it\u2019s known to make periodic close approaches to Earth. But astronomers know of no upcoming strike by this object in the foreseeable future.<\/p>\n In 2017, 3200 Phaethon came closer to Earth than it will again until 2093. At its closest in 2017, it was still about 26 times the moon\u2019s distance away. <\/p>\n Both amateur and professional astronomers watched 3200 Phaethon as carefully as they could in 2017. For example, Northolt Branch Observatories in London, England, created the animation below from images it captured in 2017.<\/p>\nWeirdly comet-like 3200 Phaethon<\/h3>\n
New research on 3200 Phaethon<\/h3>\n
How the cometary debris might form<\/h3>\n
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NASA found sodium coming off 3200 Phaethon\u2019s surface<\/h3>\n
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Sodium in the mix<\/h3>\n
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![\"Gray](\"https:\/\/earthsky.org\/upl\/2017\/12\/geminids-3200-phaethon-dust-trail-WISPR-Parker-Solar-Probe-11-5-2018.jpg\")
Inspired by the Geminid meteors<\/h3>\n
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Sodium dislodges particles<\/h3>\n
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All that, and blue, too<\/h3>\n
A potentially hazardous asteroid<\/h3>\n
Videos of 3200 Phaethon<\/h3>\n