The Finnish radio telescope aims to protect satellites from solar storms

Just 45 minutes west of Helsinki – across a forested ridge dotted with small villages and grain fields – a silent radio harbors a millimeter-wave radio telescope that has been tracking the sun’s cycles for decades now.

It’s early September, and summer in Finland has already come and gone. Thus, the Aalto University’s Metsahovi Radio Observatory may be the last place one would expect to find a window into our star. But the observatory’s 13.7-meter telescope has been constantly taking data on the sun’s middle chromosphere, which lies between the outer corona and the photosphere, since 1978. In fact, it has one of the longest records of the sun’s magnetic activity of any radio telescope on Earth.

In a country known for cold winters and dark nights, it might seem counterintuitive that such a northern latitude would work for the observatory in making some solar observations. But it does just that.

The northern location enables continuous solar monitoring for up to 60 hours at a time, enabling Mitsahovi to detect flares that can last for hours or even days. Even during the darkest winter months, the observatory can still take data as long as the sun is at least four degrees above the horizon.

The vast majority of Mitsahovi’s observations were made at wavelengths of eight millimeters.

That’s a very high wavelength, but not as high as the visible photosphere (or the solar surface), astronomer Juha Kalonki, principal engineer and laboratory director at Mitsahofi, told me here recently.

“We’ve been studying sunspots, which are regions that are darker and cooler than the surrounding photosphere,” Kalonki says. We’re studying the apparent relationship between sunspots and the radio luminosity we see in the chromosphere, he says.

One of the sun’s biggest remaining mysteries is why the photosphere is less than half that of the chromosphere. The sun’s faint outer corona observable at low-frequency radio wavelengths, and which is inaccessible to Mitsahovi, has temperatures of millions of degrees Kelvin.

Why is the corona hotter than the atmosphere?

One possibility, Kalonki says, is that charged solar particles are accelerating upward from the photosphere into the upper atmosphere and heating up the outer corona.

The faster these particle streams are accelerated, says Kalonki, the hotter their electrons become. And when they reach the corona, they are in temperatures of millions of degrees Kelvin, he says.

A long-time observer of the Earth’s eclipse will come to Finland in October to observe a partial solar eclipse.

Jay Basachoff, a professor of astronomy at Williams College in Massachusetts, tells me that high-quality timing of Mitsahofi’s radio wave observations is useful scientifically for locating small portions of sunspot regions during the eclipse itself. In this way, Basachov and others can use existing spacecraft to observe wavelengths a million times shorter, in order to work out exactly where the solar energy is emitting.

Radio radiation from the sun comes almost entirely from magnetically active regions, which appear to us largely as sunspot regions, says Basachov.

How can Mitsahovi’s observations predict what solar activity might cause problems for Earth?

When we see the radio’s brightening, Kalonki says, we can say it’s likely to be igniting. If you see brightening in the radio, it means that you are in a period that is more prone to coronal mass ejections (CMEs) or X-ray flares, he says.

But just because observatories detect flares and coronal mass ejections at the Sun does not necessarily mean that the Earth will necessarily be in the line of fire. The sun is huge and we are a small target.

Kallunki interrupts the interview to go to a large LED screen as he points to a pencil beam radio map of the solar disk, taken less than five minutes ago. Incredibly, he showed me a tiny, barely discernible bright spot in the southeast quadrant of the sun that he says is the brightest of the radio.

I see an area to the right of the image that looks a bit like a white spot. Is this brightening?

“This is the bright radio,” said Kalonko. It’s ten percent brighter than a radio than a quiet sun – when the sun is quiet, or there’s no activity.

We quickly walk outside as Kalonki showed me the outside of the 13.7-meter Radom Telescope, a radio-transparent weatherproof structure that can sometimes be obstructed by snow. But at this very age, by Finnish standards, the weather is still summer. Thus, our first stop, even before touring the workshop and the main telescope, is a small outbuilding containing the observatory’s sauna which Kalonkey assures me is very useful during the winter.

A few moments later, we entered the 13.7-meter Radom Telescope, stopped and looked at the telescope pointed toward the sun. One can easily see its almost imperceptible movements while scanning the disk of our star; Conducting thirty scans of the solar disk over a period of two minutes. It’s only early afternoon left and the telescope has already photographed a hundred maps of the sun.

Could these observations eventually become predictive enough to buy satellite operators and LEO habitats enough time to take preventive measures?

You need a network of radio ground observers to be able to do this, Kalonki says. The problem is that existing terrestrial networks only pick up on flares that have already occurred, he said.

With a terrestrial network of millimeter telescopes in place, Kalonki says it’s possible to determine whether a particular brightness would pose a threat to our satellite technology or to Earth itself.

Once the observatory detects a certain radioluminescence, Kalonki says that within days an accompanying solar flare, or solar flare, will likely erupt from the surface.

What’s next for Mitzhovy?

The next step is to get a new €1m observatory radio receiver online by 2026 which will be funded by nearby Aalto University, the observatory’s current owner.

Kalonki says that the receiver will make it possible to study the magnetic polarization of the sun’s active regions. It also has a multi-wavelength option so that we can essentially simultaneously observe near the photosphere, the middle of the chromosphere, and the upper chromosphere as well, he says. This is the next step for us, Kalonki says.

What attracts Kalonki to study the sun?

“Without the sun, we wouldn’t be able to live here; Kalonki said. So, its impact on us is palpable and every day and that’s why I love studying it,” he says.

But to monitor the fluctuations of our Sun’s 11-year magnetic cycles, the international astronomical community needs to ensure that ground-based radio observatories like Mitsahovy remain active.

As recently noted in Disaster Research Journalsolar imaging observations depend almost entirely on observations from satellites, which are themselves vulnerable to space weather.

“We will be blind as soon as extreme space weather destroys satellites,” the authors note. “It is very important that we maintain our ground-based facilities to monitor the sun.”