Ever since the Galileo spacecraft flew by Jupiter’s icy moons in 1989, scientists interested in life beyond our planet have been desperate to go back.
Europa Clipper, which blasted off from Kennedy Space Center at Cape Canaveral, is doing just that.
Galileo found clear evidence that while Ganymede, Calisto and Europa have barren frozen surfaces, beneath them likely lie vast oceans of water.
And, as far as any astrobiologist knows, where there’s water there’s a chance of life.
Kept liquid by Jupiter’s huge tidal forces, Europa’s ocean may be the Solar System’s largest.
Up to 100 miles deep, containing twice the volume of water in all Earth’s oceans, this ocean makes it a prime candidate for exploration.
After a six-year, 1.8 billion-mile journey, Europa Clipper – the largest planetary science mission ever launched by NASA – will spend four years orbiting Jupiter making flybys of its icy moon.
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It will use nine instruments to image the surface of the moon to study its atmosphere, measure the thickness of the icy crust, confirm the presence of the ocean and attempt to measure its depth and saltiness.
But before we get too excited, if there’s life on Europa, Europa Clipper won’t “see” it squirming around beneath the ice.
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First, the crust is thought to be at least 10 miles thick, too deep for the weak Sun at Jupiter to penetrate.
Without photosynthesis, if life exists, it is expected to be more akin to the bacteria that lurk in the blackness around hydrothermal vents deep on the sea floor here on Earth.
On Europa, it may live off geothermal heat, or even Jupiter’s radiation fields for energy, and simple organic molecules for food.
But we’re getting beyond Europa Clipper’s remit, which is to confirm whether the environment on the moon is compatible with these theories.
A major bonus would be whether Europa Clipper spots a plume of water erupting from the surface of the moon, which it is known to do on other icy moons. That would mean the chemicals present in the water below can be analysed directly.
“If there are life-forming conditions we expect they’re deep down in the dark,” said Dr Adam Masters, a space scientist at Imperial College London.
“So when the water comes to you, that saves a lot of hassle,” he said.
The chances of getting answers are doubled however. Dr Masters works on another mission, the European Space Agency’s Jupiter Icy Moons Explorer (JUICE).
It arrives at Jupiter shortly after Europa Clipper and will study Europa as well as another prime candidate for life, Jupiter’s moon Ganymede.
But even if these missions find tantalising chemical evidence of life, confirming its existence, let alone understanding its alien biology, would be decades away.
For that reason, one of the probes’ other objectives is to look for potential landing sites on one of these icy moons.
If Europa Clipper and JUICE finds evidence that Jupiter’s moons have the right conditions for life, the challenge for future space scientists will be figuring out how to get through miles of ice to see it.
Nearly three-quarters of American voters say US democracy is under threat, according to exit polls.
The views, compiled by Edison Research, reflect a deep anxiety as the country waits to see who its new leader will be, following a contentious campaign.
Democracy and the economy were ranked as the most important issues, with 35% citing democracy and 31% saying the economy, followed by abortion and immigration at 14% and 11% respectively.
The poll also found 73% believe democracy is in jeopardy, compared to just 25% who said it is secure. The 2020 election was followed by insurrection at the US Capitol and there has been unease about whether voters will peacefully accept whoever is chosen this year.
The exit polls also underscore the polarisation in the US, with divisions only growing starker as the campaign has worn on. Donald Trump has used increasingly dark and apocalyptic rhetoric, while Kamala Harris has warned a second Trump administration would threaten the very foundations of American democracy.
Ms Harris leads among women, while Mr Trump is more popular among male voters, the exit polls suggest. Research also shows women make up 53% of the electorate – largely unchanged from 52% in 2020.
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Trump projected to win Florida
The share of voters without a college degree – who prefer Mr Trump – is down slightly, at 57%, compared to 59% four years ago.
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Voters also said they trust Ms Harris more on issues of abortion (51% to 44%) but Mr Trump is more trusted to handle immigration (52% to 46%).
Women were more than twice as likely to name abortion as a key issue compared to men (19% of women named it as a priority, compared to 8% of men).
There were less than two percentage points between the candidates on issues of crime and who would be better at handling a crisis.
White men were more likely to favour Mr Trump (59%). But exit polls found the gap for white women was closer, with 51% supporting the Republican candidate and 47% supporting Ms Harris.
Black men and women overwhelmingly supported the Democrat nominee, at 79% and 92% respectively.
And despite comments about Puerto Rico at a Trump rally, 54% of Latino men still seem to support him, according to the polls. Almost two-thirds (62%) of Latino women supported Ms Harris.
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Trump supporters vote wearing garbage bags
The battleground states
While 52 states are theoretically up for grabs, just seven key states could decide the future of the United States.
The exit polls show Ms Harris is viewed more favourably than her Republican opponent in Michigan, Wisconsin, North Carolina and Georgia – though her ratings remain lower than Biden’s in the 2020 exit polls.
Mr Trump is viewed as more favourable than his opponent in Nevada and Pennsylvania, while the candidates are tied in Arizona.
The preliminary exit poll results are also subject to change as more people are surveyed.
No matter who wins, history will be made. Ms Harris, 60, would become the first woman, black woman and South Asian American to win the presidency.
Mr Trump, 78, would become the oldest person to be inaugurated, the only president to be impeached twice and the first former president to be criminally convicted. He would also become the first president to win non-consecutive terms in more than a century.
Voting was disrupted by bomb threats and technical problems in at least four US battleground states on election day, according to officials.
The FBI said on Tuesday evening it is “aware of bomb threats to polling locations in several states, many of which appear to originate from Russian email domains”, adding that they have all been deemed “non-credible” so far.
In the swing state of Pennsylvania, which carries the most Electoral College votes of all the battlegrounds, courts approved up to an hour extra voting time after bomb threats briefly stopped ballots being cast.
Ten polling stations in Georgia‘s Fulton County were subject to threats, with two closed and evacuated for 30 minutes on Tuesday morning.
Bomb sweeps were also carried out by police at four polling stations in DeKalb County, Georgia, with voting briefly suspended before staff were given the all-clear to return.
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Key swing states explained
Georgia’s secretary of state Brad Raffensperger echoed the FBI, saying most of the threats appeared to have been sent from Russia.
“They’re up to mischief, it seems. They don’t want us to have a smooth, fair and accurate election, and if they can get us to fight among ourselves, they can count that as a victory,” he said.
The Russian embassy in Washington denied any claims of interference, describing such allegations as “malicious slander”.
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“We would like to emphasise that Russia has not interfered and does not interfere in the internal affairs of other countries, including the United States,” it said. “As President Vladimir Putin has repeatedly stressed, we respect the will of the American people.”
In Apache County, Arizona, polls were allowed to stay open until 9pm local time – two hours after the original deadline – following bomb threats.
Adrian Fontes, Arizona’s Democratic secretary of state, said four bomb hoaxes had been delivered to polling stations in Navajo County, but they did not disrupt polling there.
Pennsylvania governor Josh Shapiro sought to assure people in his state the fake bomb threats posed “no threat to the public”.
Meanwhile in North Carolina, two counties suffered technical problems, according to the state’s board of elections.
Gardners School precinct in Wilson County reported a printer issue that saw voting suspended between roughly 6.30am and 8am, local media said.
A computer issue was also reported at Burke County Pilot Mountain voting precinct.
The US election is expected to be decided on the results in seven so-called battleground states: North Carolina, Georgia, Pennsylvania, Michigan, Wisconsin, Nevada and Arizona.
North Carolina and Georgia originally sought permission to extend polling hours beyond their original deadlines – but Sky’s partner network NBC News later confirmed both states would close on time – by 7.30pm EST (12.30am UK).
Voters were still allowed to cast their votes for a short period after that – but the polls were declared officially closed statewide.
More security threats in other battleground states
Bomb hoaxes were also reported in Michigan and Wisconsin.
Ann Jacobs, head of the Wisconsin Election Commission, confirmed two polling stations in the state capital of Madison were sent bomb threats – but neither stopped people casting their votes. She did not know of any Russian involvement.
Officials had feared disruption in North Carolina after Hurricane Helene caused devastation there last month – but authorities reported “minimal problems” aside from the minor technical glitches, with temporary precincts set up in tents in the worst-affected areas.