Researchers in the US who receive tenure produce more novel but less impactful work, according to an analysis of the output of more than 12 000 academics across 15 disciplines. The study also finds that publication rates rise steeply and steadily during tenure-track, typically peaking the year before a scientist receives a permanent position. After tenure, their average publication rate settles near the peak value.
Carried out by data scientists led by Giorgio Tripodi from Northwestern University in Illinois, the study examined the publication history of academics five years before tenure and five years after. The researchers say that the observed pattern – a rise before tenure, followed by a peak and then a steady level – is highly reproducible.
“Tenure in the US academic system is a very peculiar contract,” explains Tripodi. “It [features] a relatively long probation period followed by a permanent appointment [which is] a strong incentive to maximize research output and avoid projects that are more likely to fail during the tenure track.”
The study reveals that academics in non-lab-based disciplines, such as mathematics, business, economics, sociology and political science, exhibit a fall in research output after tenure. But for those in the other 10 disciplines, including physics, publication rates are sustained around the pre-tenure peak.
“In lab-based fields, collaborative teams and sustained funding streams may help maintain high productivity post-tenure,” says Tripodi. “In contrast, in more individual-centred disciplines like mathematics or sociology, where research output is less dependent on continuous lab operation, the post-tenure slowdown appears to be more pronounced.”
The team also looked at the proportion of high-impact papers – defined as those in the top 5% of a field – and found that researchers in all 15 disciplines publish more high-impact papers before tenure than after. As for “novelty” – defined as atypical combinations of work – this increases with time, but the most novel papers tend to appear after tenure.
According to Tripodi, once tenure and job security has been secured, the pressure to publish shifts towards other objectives – a move that explains the plateau or decline seen in the publication data. “Our results show that tenure allows scientists to take more risks, explore novel research directions, and reorganize their research portfolio,” he adds.
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The largest-ever survey of low-frequency radio emissions from satellites has detected emissions from the Starlink satellite “mega-constellation” across scientifically important low-frequency bands, including some that are protected for radio astronomy by international regulations. These emissions, which come from onboard electronics and are not intentional transmissions, could mask the weak radio-wave signals that astronomers seek to detect. As well as being damaging for radio astronomy, the researchers at Australia’s Curtin University who conducted the survey say their findings highlight the need for new regulations that cover unintended transmissions, not just deliberate ones.
“It is important to note that Starlink is not violating current regulations, so is doing nothing wrong,” says Steven Tingay, the executive director of the Curtin Institute of Radio Astronomy (CIRA) and a member of the survey team. Discussions with Starlink operator SpaceX on this topic, he adds, have been “constructive”.
The main purpose of Starlink and other mega-constellations is to provide Internet coverage around the world, including in areas that were previously unable to access it. In addition to SpaceX’s Starlink, other mega-constellations include Amazon’s Kuiper (US) and Eutelsat’s OneWeb (UK). This list is likely to expand in the future, with hundreds to tens of thousands of additional satellites planned for launch by China’s Shanghai Spacecom Satellite Technology (operator of the G60 Starlink/Qianfan constellation) and the Russian Federation (operator of the Sfera constellation).
While the effects of mega-constellations on optical astronomy have been widely studied, study leader Dylan Grigg, a PhD student in CIRA’s International Centre for Radio Astronomy Research, says that researchers are just beginning to realize the extent to which they are also adversely affecting radio astronomy. These effects extend to some of the most radio-quiet places on Earth. Indeed, several radio telescopes that were deliberately built in low-radio-noise locations – including the Murchison Widefield Array (MWA) in Western Australia and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, as well as Europe’s Low Frequency Array (LOFAR) – have recently detected interfering satellite signals.
Largest survey of satellite effects on radio astronomy data
To understand the scale of the problem, Tingay, Grigg and colleagues turned to a radio telescope called the Engineering Development Array 2 (EDA2). This is a prototype station for the low-frequency half of the Square Kilometre Array (SKA-Low), which will be the world’s largest and most sensitive radio telescope when it comes online later this decade.
Using the EDA2, the researchers imaged the sky every two seconds at the frequencies that SKA-Low will cover. They did this using a software package Grigg developed that autonomously detects and identifies satellites in the images the EDA2 creates.
Although this was not the first time EDA2 has been deployed to analyse the effects of satellites on radio astronomy data, Grigg says it is the most comprehensive. “Ours is the largest survey looking into Starlink emissions at SKA-Low frequencies, with over 76 million of the images analysed,” he explains. “With the real SKA-Low coming online soon, we need as much information as possible to understand the threat satellite interference poses to radio astronomy.”
Emissions at protected frequencies
During the survey period, the researchers say they detected more than 112 000 radio emissions from over 1800 Starlink satellites. At some frequencies, up to 30% of all survey images contained at least one Starlink detection.
“While Starlink is not the only satellite network, it is the most immediate and frequent source of potential interference for radio astronomy,” Grigg says. “Indeed, it launched 477 satellites during this study’s four-month data collection period alone and has the most satellites in orbit – more than 7000 during the time of this study.”
But it is not only the sheer number of satellites that poses a challenge for astronomers. So, too, does the strength and frequency of their emissions. “Some satellites were detected emitting in bands where no signals are supposed to be present at all,” Grigg says. The list of rogue emitters, he adds, included 703 satellites the team identified at 150.8 MHz – a frequency that is meant to be reserved for radio astronomy under International Telecommunication Union regulations. “Since these emissions may come from components like onboard electronics and they’re not part of an intentional signal, astronomers can’t easily predict them or filter them out,” he says.
Potential for new regulations and mitigations
From a regulatory perspective, the widespread detection of unintended emissions, including within protected frequency bands, demonstrates the need for international regulation and limits on unintended emissions, Grigg tells Physics World. The Curtin team is now working with other radio astronomy research groups around the world with the aim of introducing updated policies that would regulate the impact of satellite constellations on radio astronomy.
In the meantime, Grigg says, “We are in an ongoing dialogue with SpaceX and are hopeful that we can continue to work with them to introduce mitigations to their satellites in the future.”
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