• NASA's Parker Solar Probe is about to make its closest approach to the sun.
• The spacecraft will fly within 3.8 million miles of the solar surface.
• The spacecraft is collecting essential data that can help inform forecasting models on Earth.

The fastest human-made object is hurtling toward the sun at this very moment, approaching speeds of 430,000 mph — and on December 24, it's scheduled to make history.

NASA's Parker Solar Probe launched in 2018 and has completed 21 close flybys around the sun. However, its mission on Christmas Eve will be unlike any other.

At 6:53 a.m. ET, the spacecraft is set to fly the closest to the sun of any human-made object. The mission will take it closer than any previously scheduled or planned future approaches.

If all goes to plan, the uncrewed spacecraft will come within 3.8 million miles of the solar surface.

NASA anticipates the probe will experience temperatures of 1,800 degrees Fahrenheit, which shouldn't be an issue since the spacecraft's protective heat shield is designed to withstand temperatures over 2,500 degrees Fahrenheit.

Yes, 3.8 million miles is far by Earth's standards, but it's ridiculously close when you're out in deep space.

It's like if you put the Earth and sun at opposite ends of an American football field: "Parker Solar Probe is on the 4-yard line approaching the sun," Joe Westlake, Director of NASA's Science Mission Directorate's Heliophysics Division, told 6abc Philadelphia.

"It is getting so close that we're actually in the sun's upper atmosphere. We're actually touching the sun with humanity's first mission to a star," Westlake added.

The moment NASA has been waiting for

The Christmas Eve flyby is the moment the mission has been building up to for years.

"This close approach is only possible because of the mission's orbital design," a NASA spokesperson told Business Insider via email.

"The spacecraft had to shed a lot of orbital energy to get this close to the sun, so that's why it took several years," the spokesperson added.

Over the years the Parker Solar Probe, about the size of a small car, has made increasingly close flybys.

For example, in September 2020, it flew within 8.4 million miles of the solar surface. By September 2023, it reached within 4.5 million miles.

When the spacecraft makes these close approaches, it cuts communication with Earth and flies autonomously, guiding itself through the sun's harsh upper atmosphere until it's far enough away to reestablish coms.

NASA last heard from Parker Solar Probe on December 22 and expects to hear from it again around midnight between Thursday and Friday, Nour Rawafi, Parker Solar Probe project scientist at Johns Hopkins Applied Physics Lab, said during a recent NASA livestream.

While flying so close to the sun doesn't hold any promise of discovering alien life there or paving the way for future crewed missions to walk on the solar surface, the Parker Solar Probe's mission is, arguably, more important.

Here's what you need to know about this historic mission and how it could help humanity solve some of the world's biggest questions.

Parker Solar Probe is helping us answer the big questions

It may appear calm and quiet from far away, but the sun is a turbulent sphere of activity. It's got solar flares and massive eruptions that fire fast-moving, charged particles deep into our solar system.

"Without that activity, we would not exist. That activity is really necessary for life to kick off," Rawafi said during NASA's livestream.

So, on a grand scale, understanding how our sun works can help us better understand how life originated on Earth and where it might exist elsewhere in the universe.

Also, by studying our own star up close, we can learn how other stars in the universe interact "with the billions and billions of other planets that may or may not be like our own planets," Alex Young, associate director for science communication in NASA's Heliophysics Science Division, said during the livestream.

Wishing for the biggest explosion ever

Rawafi said the best gift the sun could give scientists during Parker Solar Probe's coming approach is "one of the strongest explosions ever."

The sun is currently at a solar maximum — a period of peak solar magnetic activity lasting one to two years and causing powerful flares, eruptions, and ejections.

Sometimes, the charged particles from these eruptions reach Earth. When that happens, it can disrupt satellites, mess with GPS, and subsequently ground flights. It can also expose astronauts to high levels of space radiation.

As we continue to launch more satellites and people into space, these solar events are a growing threat. Yet, scientists don't have a highly accurate forecasting model for warning satellite operators and astronauts far in advance.

That's why Rawafi wants a big explosion: The probe would be in a perfect position to study the event mere moments after it occurs, offering scientists swaths of data that could help inform and improve forecasting models.

Parker Solar Probe has already collected so much data during its years of operation that it will take decades to study it all, Rawafi said at the American Geophysical Union annual meeting in early December.

According to NASA, the spacecraft is scheduled to complete 24 orbits around the sun, with its last two planned for 2025.

• A 7.0-magnitude earthquake struck off the shore of Northern California Thursday morning.
• Tsunami warnings have been lifted across northern California and southern Oregon.
• Aftershocks are ongoing, and there's a small chance they could outdo the first quake.

A major earthquake struck near California's coast on Thursday, and aftershocks are still ongoing.

The 7.0-magnitude earthquake struck at about 10:44 a.m. Pacific Time. Its epicenter was offshore, about 62 miles west-southwest of Ferndale, California, according to data from the United States Geological Survey.

The USGS website reported more than 35 smaller quakes across that area over the ensuing three hours, of magnitudes ranging from 2.5 to 4.7, including two quakes that occurred inland.

"There's been quite a lot of aftershocks," Harold Tobin, Washington's state seismologist and the director of the Pacific Northwest Seismic Network, told Business Insider.

As of Thursday afternoon, the USGS forecasts up to 130 aftershocks with a magnitude of 3 or higher within the next week, and a 53% chance of aftershocks larger than magnitude 5.

"It's perfectly plausible that there could be a larger aftershock or more than one larger aftershock," Tobin said.

The USGS estimates the odds are 1 in 100 of an aftershock with a magnitude of 7 or greater.

The fault that slipped

The fault region which produced the 7.0 earthquake is a very seismically active one.

It's called the Mendocino triple junction because three different tectonic plates meet there: the Pacific, North American, and Juan de Fuca plates.

It's right between two notorious earthquake zones, at the northern end of the San Andreas fault and the southern end of the Cascadia Subduction Zone. The CSZ has some of the planet's greatest seismic potential, capable of producing quakes as big as 9.0.

The Mendocino triple junction, however, is less impressive.

"Somewhere in the magnitude sevens range is about as big as things seem to get out there," Tobin said.

The region has produced five earthquakes of magnitude 7 or larger in the past century, according to USGS.

The Thursday quake could have slightly increased the chance of other earthquakes along adjacent faults by increasing stress in those areas.

"It's unlikely that it had a really large, significant impact" on those fault systems, though, Tobin said. The odds are "not zero, but very low," he added.

Tsunami scare

The initial quake triggered tsunami warnings and evacuations — which have since been canceled — along the coast of northern California to southern Oregon, including the San Francisco Bay Area.

The warnings lasted about an hour. The National Tsunami Warning Center canceled them around 11:54 a.m. local time, saying there was no longer a threat.

Most likely, the reason there was no tsunami is that the earthquake came from plates moving side-by-side against each other. This is called a strike-slip earthquake. Because the motion was mostly horizontal, and not vertical, it didn't push the ocean above upward to create a wave.

Even so, the warning was "warranted," Tobin said.

"Until we know enough parameters of the earthquake and can verify whether there is or isn't an actual wave, it's wise to have those warnings," he added.

Possible earthquake damage

The USGS also reported on X a "low likelihood of shaking-related fatalities. Some damage is possible and the impact should be relatively localized."

Governor Gavin Newsom declared a state of emergency for three counties in Northern California which were near the offshore epicenter of the quake.

"We're concerned about damage," he said in a press briefing, adding that the declaration would allow the state to "provide more resources."

According to CNN, about 10,000 homes and businesses in Humboldt County — the area nearest the epicenter — were without power immediately after the large quake. As of Thursday afternoon, though, PowerOutage.us reported fewer than 500 customers without power there.

Newsom said that "early damage assessments are being made," but that the state had no additional information to share yet.

This is a developing story, check back for more information.

• Parts of Siberia's landscape are a ticking time bomb.
• Giant craters started mysteriously appearing 10 years ago.
• A team of scientists think they finally know why.

Tucked away in the frigid northern corner of Siberia are giant craters, some deep enough to fit a 15-story building. Scientists observed the first crater in 2014 and have found about 20 more in the years since.

It's been fairly clear from the beginning that the craters are caused by some type of explosion deep underground. What's triggering the explosions is a topic of debate — one that Ana Morgado, a chemical engineer at the University of Cambridge, thinks she and her colleagues have settled.

If their theory is correct, it would mean these types of exploding craters are rare and only form under specific geologic conditions, so there's no risk of something similar showing up in, say, downtown Manhattan.

Their theory also ties these massive eruptions to climate change. As the planet continues to warm, more craters will likely erupt. When this happens, it releases a highly potent greenhouse gas into the atmosphere, which in turn contributes to climate change.

The mysterious case of Siberia's exploding craters

The colder nooks of the world, in places like Siberia and northern Canada, have a subsurface layer of soil called permafrost that's been permanently frozen for millennia. As global temperatures climb, pockets of permafrost are thawing worldwide.

This has led to some spectacular discoveries like a perfectly preserved 30,000-year-old squirrel in Canada and a 46,000 year-old worm in Siberia. It's not just ancient squirrels and worms hiding in permafrost.

Concentrated amounts of the highly explosive greenhouse gas methane are trapped deep underground in the permafrost in ice-like solids called methane hydrates.

Researchers widely agreed that when these hydrates are damaged, they release methane gas, which is what's triggering the explosions in Siberia.

How the hydrates are damaged in the first place, though, is less clear.

Existing theories suggest that warming permafrost, as a result of the warming Arctic, could ultimately destabilize the hydrate layer, releasing explosive methane gas.

"That was the initial idea, and we didn't question it at all at the beginning," Morgado told Business Insider. "What we questioned was that: Okay, you're saying that that is the case, but you don't present a physical model that can explain that. So no math."

When the team tried matching the math with the observations, they found that it would take centuries for the process to trigger an explosion. The Arctic had only been significantly warming over decades.

"So either something else was happening or magnifying this effect," Morgado said in an email.

The team found the missing piece to their puzzle when they learned of past geological surveys that had identified pools of liquid water, called cryopegs, just above the methane hydrates in Siberia.

What's causing the ground to erupt in Siberia

Normally, the cryopegs are stable. Morgado and the team realized that the summer would threaten this stability.

In summer, frozen soil at the surface melts. That meltwater is then pulled down toward the cryopegs via a process called osmosis — the same process that helps water climb against gravity through tall plants.

Osomis was the magnifying effect the researchers were looking for.

With longer, warmer summers in recent years, enough meltwater is available for long enough periods that it's being driven down to the cryopegs on timescales that matched the observations, Morgado said.

Once the meltwater reaches the cryopegs, it's over.

The meltwater increases the pressure inside the cryopegs, just like adding more water to a water balloon. That pressure cracks the soil leading to the surface, which triggers a drastic reverse in pressure. And that pressure change is what damages the methane hydrates, triggering an explosion.

More exploding craters to come

Siberia will likely have more explosive craters in the coming years as global temperatures continue to warm. That's a problem because the methane these explosions release is a highly potent greenhouse gas, which helps drive global temperatures up even more.

It's unclear exactly how much methane these explosions release, but in the grand scheme of climate change, they're a small matter. Thawing permafrost is a larger concern because it contains concentrations of not only methane but also carbon dioxide that is released into the atmosphere when it melts.

Siberia isn't the only place in the world with permafrost.

If the team's theory is correct, it's possible, but unlikely, that other places with permafrost will start erupting the way Siberia has, Morgado said.

"It would need to be very specific that you would have this in another place," Morgado said, adding, "Luckily we are not seeing the entire world, or the entire Arctic, bursting into craters."