It’s been apparent for a long time that far more astronomical data exist than anyone has had time to examine thoroughly. That’s a reassuring thought, given the uses to which we can put these resources. Ponder such programs as Digital Access to a Sky Century at Harvard (DASCH), which draws on a trove of over half a million glass photographic plates dating back to 1885. The First and Second Palomar Sky Surveys (POSS-1 and POSS-2) go back to 1949 and are now part of the Digitized Sky Survey, which has digitized the original photographic plates. The Zwicky Transient Facility, incidentally, uses the same 48-inch Samuel Oschin Schmidt Telescope at Palomar that produced the original DSS data.
There is, in short, plenty of archival material to work with for whatever purposes astronomers want to pursue. You may remember our lengthy discussion of the unusual star KIC 8462852 (Boyajian’s Star), in which data from DASCH were used to explore the dimming of the star over time, the source of considerable controversy (see, for example, Bradley Schaefer: Further Thoughts on the Dimming of KIC 8462852 and the numerous posts surrounding the KIC 8462852 phenomenon in these pages). Archival data give us a window by which we can explore a celestial observation through time, or even look for evidence of technosignatures close to home (see ‘Lurker’ Probes & Disappearing Stars).
But now we have an entirely new class of archival data to mine and apply to the study of exoplanets. A just published paper discusses how previously undetectable data about stars and exoplanets can be found within the archives of radio astronomy surveys. The analysis method has the name Multiplexed Interferometric Radio Spectroscopy (RIMS), and it’s intriguing to learn that it may be able to detect an exoplanet’s interactions with its star, and even to run its analyses on large numbers of stars within the radio telescope’s field of view.
We are in the early stages of this work, with the first detections now needing to be further analyzed and subsequent observations made to confirm the method, so I don’t want to minimize the need for continuing study. But if things pan out, we may have added a new method to our toolkit for exoplanet detection.
The signature finding here is that the huge volumes of data accumulated by radio telescopes worldwide, so vital in the study of cosmology through the analysis of galaxies and black holes, can also track variable activity of numerous stars that are within the field of view of each of these observations. What the authors are unveiling here is the ability to perform a simultaneous survey across hundreds or potentially thousands of stars. Cyril Tasse, lead author of the paper in Nature Astronomy, is an astronomer at the Paris Observatory. Tasse explains the range that RIMS can deploy:
“RIMS exploits every second of observation, in hundreds of directions across the sky. What we used to do source by source, we can now do simultaneously. Without this method, it would have taken nearly 180 years of targeted observations to reach the same detection level.”
The researchers have examined 1.4 years of data collected at the European LOFAR (Low Frequency Array) radio telescope at 150 MHz. Here low frequency wavelengths from 10 to 240 MHz are probed by a huge array of small, fixed antennas, with locations spread across Europe, their data digitized and combined using a supercomputer at the University of Groningen in the Netherlands. Out of this data windfall the RIMS team has been able to generate some 200,000 spectra from stars, some of them hosting exoplanets. While a stellar explanation is possible for star-planet interactions, this form of analysis, say the authors, “demonstrate[s] the potential of the method for studying stellar and star–planet interactions with the Square Kilometre Array.” LOFAR can be considered a precursor to the low-frequency component of the SKA.
Here we drill down to the planetary system level, for among the violent stellar events that RIMS can track (think coronal mass ejections, for example), the researchers have traced signals that produce what we would expect to find with magnetic interactions between planet and star. Closer to home, we’ve investigated the auroral activity on Jupiter, but now we may be tracing similar phenomena on planets we have yet to detect through any other means.
Image: Artistic illustration of the magnetic interaction between a red dwarf star such as GJ 687, and its exoplanet. Credit: Danielle Futselaar/Artsource.nl.
Let’s focus for a moment on the importance of magnetic fields when it comes to making sense of stellar systems other than our own. The interior composition of planets – their internal dynamo – can be explored with a proper understanding of their magnetosphere, which also unlocks information about the parent star. That sounds highly theoretical, but on the practical plane it points toward a signal we want to acquire from an exoplanetary system in order to understand the environments present on orbiting worlds. And don’t forget how critical a magnetic field is in terms of habitability, for fragile atmospheres must be shielded from stellar winds so as to be preserved.
At the core of the new detection method is cyclotron maser instability(CMI), which is the basic process that produces the intense radio emissions we see from planets like Jupiter. CMI is an instability in a plasma, where electrons moving in a magnetic field produce coherent electromagnetic radiation. Here is a link to Juno observations of these phenomena around Jupiter.
Detecting such emissions, RIMS can point to the presence of a planet in a stellar system. Working with radio observations, we can move beyond modeling to sample actual field strengths, which is why radio emissions (not SETI!) from exoplanets have been sought for decades now. Finding a way to produce interferometric data sufficient to paint a star-planet signature is thus a priority.
Exoplanetary aurorae would indicate the existence of magnetospheres, and that’s no small result. And we may be making such a detection around a star some 14.8 light years away, says co-author Jake Turner (Cornell University):
“Our results indicate that some of the radio bursts, most notably from the exoplanetary system GJ 687, are consistent with a close-in planet disturbing the stellar magnetic field and driving intense radio emission. Specifically, our modeling shows that these radio bursts allow us to place limits on the magnetic field of the Neptune-sized planet GJ 687 b, offering a rare indirect way to study magnetic fields on worlds beyond our Solar System.”
There are also implications for the search for life elsewhere in the cosmos. Turner adds:
“Exoplanets with and without a magnetic field form, behave and evolve very differently. Therefore, there is great need to understand whether planets possess such fields. Most importantly, magnetic fields may also be important for sustaining the habitability of exoplanets, such as is the case for Earth,”
Using low-frequency radio astronomy, then, we turn a telescope array into a magnetosphere detector. Researchers have also applied the MIMS technique to the French low frequency array NenuFAR, located at the Nançay Radio Observatory south of Paris, detecting a burst from the exoplanetary system HD 189733 that was described recently in Astronomy & Astrophysics. As with another possible burst from Tau Boötes, the team is in the midst of making follow-up observations to confirm that both signals came from a star-planet interaction. If the method is proven successful, such interactions point to a new astronomical tool.
The paper is Tasse et al., “The detection of circularly polarized radio bursts from stellar and exoplanetary systems,” Nature Astronomy 27 January 2026 (abstract). The earlier paper is Zhang et al., “A circularly polarized low-frequency radio burst from the exoplanetary system HD 189733,” Astronomy & Astrophysics Vol. 700, A140 (August 2025). Full text.
Admittedly I haven’t read the paper, however I can’t help thinking that any signal is going to be very ambiguous. Distinguishing poorly understood stellar magnetic activity from poorly understood exoplanet magnetism must pose quite the puzzle. Teasing apart these overlapping phenomena will be difficult.
It’s different with radio frequencies since these can be easily differentiated. Solar flare in the Gegahertz and exo Jupiter in the megahertz. Also the tighter spirals of the magnetic fields the Jupiter sized exoplanet are mostly circular polarized and the solar flares mostly not. Google AI. Exo Earth magnetic fields would be harder to detect, but not “the Stellar interaction shortcut” where the exo Earth and stars magnetic fields are couples cause aurora’s on the red dwarf star “causing the planet to act like a conductor strengthening the planets auroral radio emission.” ibid. The reason being that the red dwarf system is smaller and therefore exoplanet more closer so a magnetic bridge forms and electrons flow back and forth. ibid.
Of course the problem with Earth sized exoplanets near red dwards are in the Hill sphere and can’t have a Moon and are also tidally locked so they can’t have a fast rotation and any magnetic fields. Jupiter sized exoplanets this idea works.
Now hold on, Geoffrey, there is more to that story than just dead planets…
“Super-Earth exoplanets may have built-in magnetic protection from churning magma.”
“Magma oceans and strong magnetic fields on super-Earths.”
https://earthsky.org/space/magnetic-fields-on-super-earths-exoplanets-habitability-astrobiology/
https://www.universetoday.com/articles/deep-magma-oceans-could-help-make-super-earths-habitable
From large Supe-Earths to small Mars-sized planets could have large magnetic fields:
Induction heating, caused by changing stellar magnetic fields inducing electric currents in planetary mantles, is a significant energy source for planets orbiting strongly magnetized M dwarfs. This process can exceed radioactive decay and tidal heating, potentially triggering magma oceans and intense volcanic activity, particularly on close-in planets.
Key Aspects of Induction Heating on M Dwarf Planets:
Mechanism: Strong, kiloGauss-range stellar magnetic fields induce eddy currents in the conducting mantle of orbiting planets, leading to energy dissipation.
Conditions for Intensity: It is most effective when the planet’s orbit is inclined relative to the star’s rotation/dipole axis, or if the star’s dipole is tilted.
Impact on Rocky Planets: Studies suggest this heating can be substantial for planets like those in the TRAPPIST-1 system (e.g., TRAPPIST-1c), potentially keeping the surface in a molten state.
Comparison to Other Heat Sources:
In some scenarios, induction heating can be more powerful than tidal heating, especially in single-planet systems where orbital eccentricity decays quickly.
Self-Limiting Behavior:
While it can cause extreme volcanism, the resulting magma oceans (which are better conductors) may increase the electrical conductivity, creating a “skin effect” that limits deeper penetration of the magnetic field, thus somewhat limiting total heat input.
Habitability Implications:
While it can drive, or sometimes prevent, volcanic activity, excessive induction heating may limit the habitability of planets, notes Centauri Dreams.
https://www.centauri-dreams.org/2021/08/10/can-m-dwarf-planets-survive-stellar-flares/
This mechanism is particularly relevant for close-in, terrestrial planets orbiting active, low-mass M dwarf stars.
https://share.google/aimode/DpXCSnGYriV2adNQQ
Dead planets? Maybe I’ve said something like that in the past and I am not so confident about that if there is water detected in a super Earth atmosphere. I do think without oxygen in that atmosphere the probability of life is low, but this is another topic. The main idea of the physics of planetary magnetic fields is that there needs to be a fast rotation which causes Coriolis deflection of charged particles. All planetary magnetic fields in our solar system, Earth, Jupiter, Saturn, Uranus, Neptune use Coriolis deflection to make their magnetic fields. Mercury is the exception, but it does not have a strong magnetic field and has a large iron core. Mars did have a stronger magnetic field, but the core dried.
To be precise Earth’s magnetic field is much weaker than Jupiter’s so it would be hard to detect any radio frequency from it on it’s own which would be the case around G class stars which did not have any magnetic bridge to help strengthen the field since an Earth sized exoplanet in the life belt around a G class star would be too far away from its star to have a magnetic bridge like a Red dwarf star, so these would not be easy to detect so it is beneficial to take a skeptical attitude since sometimes an idea does not work in all cases. We still might be able to detect a magnetic field in that case but it would be harder to detect. Google AI
An interesting post Paul
and while were on the subject new data about Jupiter and an interesting new Cool exoplanet to have a look into as well.
The size and shape of Jupiter
https://www.nature.com/articles/s41550-026-02777-x.epd
A Cool Earth-sized Planet Candidate Transiting a Tenth Magnitude K-dwarf From K2
https://iopscience.iop.org/article/10.3847/2041-8213/adf06f
Cheers Edwin
It is certainly convenient that much of this photographic data has been digitized, making it available for immediate access through the internet. It should be kept in mind, however, that the original medium, glass photographic plates, contain positional information that cannot be precisely digitized, so these photos must still be preserved.
I spent much of my time as an astronomy student in the 1970s hunched over a measuring engine extracting highly precise stellar positional information from star images. The accuracy of these positions was limited only by the grain size of the photographic emulsions and the ability to machine the mechanical components of the device. Using a microscope, it was possible to measure positions on the plates to within a micron, and most of the systematic and random errors inherent in the data could be reduced with modeling and statistical methods. Using these techniques, it was possible to make x,y position measurements with accuracies in the sky on the order of milliarcseconds!
Although modern automated scanners and digitizers can capture these minute displacements, simply reproducing the plates for visual display on a monitor may not be able to achieve the accuracy or precision needed for positional astronomy, particularly parallax work. A further complication is introduced if the digital data is compressed for economy in transmission or display. Stellar images are not dimensionless points superimposed on an empty background, they are complex statistical averages due to both the chemistry of the emulsion, atmospheric scintillation, instrumental effects, and the wave nature of light. A typical star under a microscope is not a dot, but a blob on the emulsion resembling a negative photograph of a globular cluster, and the size of that blob is a function of the star’s magnitude. Even the measurer’s own eyes introduce a personal bias that must be modeled out.
Dealing with these problems is what most of astrometry was all about. Hopefully, many of these issues have been at least partially resolved by the introduction of digital sensors and scanners, but the old plates still have great value because many of them go ‘way back; they record a position as it existed a long time ago, sometimes all the way back to the 19th century. The phenomenal dimensional stability of gel on glass allows us to compare extremely slow motions as they accumulate over long periods of time. Much of this data cannot be duplicated today, we would have to wait again for an equivalent amount of time to achieve it.
In addition to motion, the old plates contain evidence of transient phenomena which may be of interest, such as changes in brightness, or in the shapes of extended sources such as nebulae, or the passing thru of relatively nearby objects. I recall how during my measuring days I was often struck by how much trash was flying around the solar system: long time exposures show stars as blobs, asteroids as short fuzzy caterpillars, meteors as long streaks.
There is another property of these old plate archives which make them particularly valuable. Astronomers used the same techniques and emulsions for years, so the data is often directly comparable across decades of time. In other words, it is possible to directly compare an image taken in 1920 to one exposed forty years later, the individual differences of seeing, aperture, optics etc can be modeled out because reference stars scattered about each field (measured with highly precise alternate methods) can be used to establish a baseline to which all astrographic imagery can be reduced mathematically. For example, it is possible to determine changes in the brightness AND color index of a star by comparing plates taken decades apart, through different telescopes, under different observing conditions.
Occasionally I hear or read stories about how much pressure there is on astronomical archivists to digitally copy and dispose of the extensive plate libraries which have been cataloged and stored by astronomical institutions. Curating and preserving these collections is expensive, but there is an enormous amount of information still locked up in those plates which may be lost forever if not properly managed, not to mention additional data which may be extracted by potential future technologies.
@Henry
Funnily enough, we had a very similar problem in biology as late as teh early 2000s. Films were used to record the emissions of blobs RNA with phosphorus isotopes to emit the radiation to darken the film. The amount of the RNA, indicative of gene expression, increased the size and density of the blob. Whilst the general layout was a grid, the exact position of each blob would be displaced in various ways, and it required hand arranging enclosing grids on the digitized films. Very tedious work when the idea was to scale up production. It was made worse by the need to reuse the films with washing to save money, which introduced new errors due to incomplete washes. Fortunately, newer technology came to the rescue: microarrays with 2-color dyes and far better software to measure the amount of each dye and, by extension, the amount of RNA in pre- and post-treatment gene expression tissue. A similar issue would have applied to various protein experiments using electrophoresis with radioactive carbon isotopes to separate proteins and measure their abundances. So much tedious bench work that is no longer feasible when scaling up experiments and the number of samples.