Seven planets line up in the sky next month. This is what it really means

Stargazers will be treated to a rare seven-planet alignment on February 28, when Mercury joins six other planets already visible in the night sky. Here’s why it’s important to scientists.

Look up at the sky on a clear night in January and February and you may be in for a treat. Six planets – Venus, Mars, Jupiter, Saturn, Uranus and Neptune – are currently visible in the night sky. For just one night in late February, they will be joined by Mercury, a rare seven-planet alignment visible in the sky.

But such events are not just a spectacle for stargazers – they can also have a real impact on our solar system and offer the potential to gain new insights into our place in it.

The eight major planets in our solar system orbit the Sun in the same flat plane, and all at different speeds. Mercury, the closest planet to the Sun, completes one orbit – one year for the planet – in 88 days. Earth’s year is of course 365 days, while at the upper end Neptune takes a full 60,190 days, or about 165 Earth years, to complete a single revolution of our star.

The different speeds of the planets mean that several of them can sometimes be roughly lined up on the same side of the Sun. From Earth, if the orbits are just right, we can see several planets in our night sky at the same time. On rare occasions, all the planets will line up so that they all appear in our night sky together along the ecliptic, the path that the Sun traces.

Mercury, Venus, Mars, Jupiter and Saturn are all bright enough to be visible to the naked eye, while Uranus and Neptune require binoculars or a telescope to spot.

In January and February we can see this event take place. The planets are not aligned so they will appear in an arc across the sky due to their orbital plane in the solar system. On clear nights in January and February, all the planets except Mercury will be visible—an event sometimes called a planetary parade. But on February 28 – weather permitting – all seven planets will be visible, a spectacular sight for observers on Earth.

“There’s something special about seeing the planets with your own eyes,” says Jenifer Millard, science communicator and astronomer at Fifth Star Labs in the UK. “Yes, you can go on Google and get a more spectacular picture of all these planets. But when you look at these objects, these are photons that have traveled millions or billions of miles through space to hit your retina.”

While fascinating to observe, do such adjustments have any impact here on Earth? Or could they be needed to increase our understanding of our solar system and beyond?

In fact, says Millard, “it’s just a coincidence that they happen to be in this position of their trajectories”. And while there have been suggestions by some scientists that planetary alignments might cause impacts on Earthis the scientific basis for most of these claims weak or non-existent.

However, in 2019, researchers suggested that planetary alignments could have an impact on solar activity. One of the most important outstanding questions about the Sun is what drives its 11-year cycle between periods of peak activity, known as solar maximum (which we is at the moment), and periods of weakest activity, solar minimum. Frank Stefani, a physicist at the Helmholtz-Zentrum research center in Dresden-Rossendorf, Germany, believes that the combined tidal forces of Venus, Earth and Jupiter may be the answer.

While the tidal pull of each planet on the Sun is extremely small, Stefani says that when two or more of the planets are aligned with the Sun — known as a syzygy — they can combine to cause small rotations inside the star, called Rossby waveswhich can drive weather events.

“On Earth, Rossby waves cause cyclones and anticyclones,” says Stefani. “We have the same Rossby waves in the Sun.” Stefani’s calculations showed that the alignment of Venus, Earth, and Jupiter would cause a periodicity for solar activity of 11.07 years, which is nearly the length of ​​solar cycles as we see.

Not everyone is so sure about the idea, and some note that solar activity can already be explained by processes in the Sun alone. “The observational evidence suggests that the planets that directly cause the solar cycle just don’t happen,” said Robert Cameron, a solar scientist at the Max Planck Institute for Solar System Research in Germany, who published a paper. on the subject in 2022. “There is no evidence of any synchronization.”

But there are other, far less contentious, quirks of planetary alignments that certainly have an impact on us: their utility for scientific observations, especially in terms of exploring the solar system.

It is difficult to reach the outer planets with a spacecraft because these worlds are so far away, billions of miles, and it would take decades to reach. But using the gravity of a well-placed planet, such as Jupiter, to hurl a spacecraft outward can dramatically reduce travel time, something no spacecraft has done better than NASA’s Voyager vehicles.

In 1966, a Nasa scientist named Gary Flandro calculated that there would be one alignment of the outer four planets – Jupiter, Saturn, Uranus and Neptune – in 1977 would make it possible to visit all four in just 12 years, compared to 30 years if they were not aligned. This fortuitous alignment, which occurs only once every 175 years, led Nasa in 1977 to launch the twin spacecraft Voyager 1 and 2 on a “Grand Tour” of the outer solar system.

Voyager 1 flew by Jupiter in 1979 and Saturn in 1980, avoiding Uranus and Neptune because the scientists wanted to fly by Titan, Saturn’s fascinating moon, and could not do so without destroying the slingshot effect.

“It worked great,” says Fran Bagenal, an astrophysicist at the University of Colorado, Boulder in the US and a member of the Voyager science team. “If Voyager 2 had left in 1980, it would have taken until 2010 to get to Neptune. I don’t think it would have won support. Who’s going to fund something like that?”

It is not only in our solar system that planetary alignments are useful. Astronomers use alignments to investigate many different aspects of the universe, and none more so than in the discovery and study of exoplanets, worlds that orbit stars other than the Sun.

The dominant way to find such worlds is known as transit method: When an exoplanet passes in front of a star from our point of view, it dims the star’s light so that its size and orbit can be discerned.

Thanks to this method, we have discovered many planets orbiting certain stars. Trappist-1, a red dwarf star located 40 light years from Earth, has seven earth-sized planets that all pass the star from our point of view. The planets in that system are actually in resonance with each other – meaning that the outermost planet completes two orbits for every three orbits of the next planet inward, then four, six, and so on. This means that there are periods when several planets in the system align in a straight line, something that does not happen in our solar system.

By using transit, we can study the existence of atmospheres on planets like these. “If a planet with an atmosphere passes in front of a star, that alignment means that starlight passes through the planet, and the molecules and atoms in the planet’s atmosphere absorb light at certain wavelengths,” said Jessie Christiansen, an astronomer at Nasa Exoplanet. Science Institute at the California Institute of Technology.

This makes it possible to identify different gases such as carbon dioxide and oxygen. “The vast majority of our atmospheric composition analysis is due to adjustments,” she says.

Much larger alignments can let us probe the distant universe, namely the alignments of galaxies. It is difficult to observe galaxies in the very early universe because they are so faint and far away. But if a large galaxy or cluster of galaxies passes between our line of sight with a much more distant early galaxy, its great gravity can magnify the light from the more distant object, allowing us to observe and study it, a process called gravitational lensing.

“These are huge adjustments across the scale of the universe,” says Christiansen. They are used by telescopes such as the James Webb Space Telescope to observe distant stars and galaxies such as Ear partthe most distant known star from Earth. The light seen by the telescope from the star came from the first billion years of the universe’s 13.7 billion year history and was only visible due to gravitational lensing.

And then there are some more novel uses of alignments, such as investigating the existence of extraterrestrial life, in solar systems where the exoplanets pass in front of each other from our point of view.

In 2024, graduate student Nick Tusay at Pennsylvania State University in the United States used these adaptations to look for contagious communication being sent between worlds in the Trappist-1 system, like how on earth we send signals to planets like Mars in our solar system to talk to rovers and spacecraft. “Anytime two planets line up, it can be interesting,” says Tusay.

On this occasion the searches were short. But an alien civilization searching towards our own solar system might use similar adjustments for the same purpose. While this month’s planetary parade depends on your point of view – any two planets in our system can align if you’re positioned at the right angle – it’s not impossible to imagine someone else on the other end watching.

“Perhaps another alien civilization may see this as an opportunity to conduct their own investigations,” says Tusay.

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