There is an almost unknown area on the border between the atmosphere and space – Soon it can be explored by a hovering mini-device

Terrestrial there is a region in the atmosphere that is almost unknown to man. Now researchers have developed a measuring device that could be used to study this place called the ignorosphere.

The officially named region is the ionosphere–thermosphere, and it extends from 80 kilometers to an altitude of about 600 kilometers, i.e. at the border between the atmosphere and outer space.

It is too high for probes and weather observation balloons, and on the other hand too low for satellites. There is so much oxygen that satellites catch fire there.

Harvard of the university Ben Schafer with colleagues introduced recently in the journal Nature of a feather-light device that could transport measuring instruments to this little-explored region of the atmosphere.

The device uses a phenomenon called photophoresis. When gas particles are heated with light, they start to move. The particles bounce more strongly from the hot side of the object, creating constant momentum and lift.

So the device would float in the air with just the power of sunlight. The phenomenon only works in strong low pressure, but that is exactly what is found in the upper atmosphere.

The first times the phenomenon was noticed already 150 years ago, but applications for it have hardly been found.

Now Schafer and his team built a centimeter-wide device, which consists of two perforated aluminum oxide plates. A layer of chrome was added to the lower surface of the device to absorb more sunlight. When the device is hit by sunlight, the temperature difference between the top and bottom surfaces creates a lift that exceeds the weight of the device.

The researchers tested their device in a laboratory in a low-pressure chamber, where they created conditions similar to the upper atmosphere. The device was illuminated with an amount of light that corresponds to sunlight at an altitude of 60 kilometers. The light made the device momentarily float.

The problem is that the device must be very light to float. The researchers calculated that in the upper atmosphere it would be able to lift a maximum load of ten milligrams – that is, the weight of a couple of grains of sand. However, it would be enough for a tiny solar cell and sensors that measure wind speed, air pressure and temperature.

After the sun goes down, the device could stay in the air by utilizing the heat radiating from the earth’s surface.

Alternatively, the device could be used for communication. Devices equipped with radio antennas would form a floating network with a data transmission capacity comparable to a small satellite. The delay would be smaller because the devices hover closer to the ground.

Later, equipment could be sent even to Mars. The Earth’s upper atmosphere resembles the gas atmosphere of Mars in many ways, and sending small devices into space is significantly cheaper than traditional probes.

Floating the devices are interesting in terms of technology, but they alone do not eliminate the problems related to the research of the ignorosphere, says the professor of space physics at the University of Helsinki Minna Palmroth.

The devices are designed for an altitude of about 80 kilometers, but there would be research to be done especially in the upper part of the ignorosphere, where the atmosphere and space interact most strongly.

Temperature, pressure and particle density change suddenly when you move from the atmosphere to the vacuum of space. There are also large electrical currents in this borderland that heat the atmosphere and lift it up into orbit. The phenomenon is called Joule heating.

“Heating affects satellites in low orbits, which can lose altitude due to increased friction. Since Joule’s heating is unknown, situations happen completely unexpectedly. The last time this happened was in 2022, when 38 satellites suddenly fell into the atmosphere,” says Palmroth.

In the coming years, the importance of the ignorosphere will grow even more. Satellites should be brought down from their orbits more efficiently, so that they don’t stay there accumulating space junk. In the Ignorosphere, friction cleans the satellites by itself, but on the other hand, their lifetime can be too short in an unpredictable area.

“If there is an area on Earth that we don’t know yet, I think it should be explored. We can’t leave uncharted areas on our planet, especially if we want to exploit them in the future.”

Published in Tiede magazine 11/2025.