![]() At a powerful radio telescope, the hunt for signals from intelligent extraterrestrial life is on From these, Li's team was able to derive much lower drift rates - plus or minus 0.27 nHz for the low-eccentricity orbits and plus or minus 0.44 nHz for the high-eccentricity orbits. The imagined planets were placed into 20 groups, each consisting of 5,286 worlds, split into 10 groups with nearly circular orbits and 10 groups with increasingly non-circular (known as eccentric) orbits. So, to try and avoid any biases, Li's team also measured the maximum drift rate of over 5,000 simulated planets that we might expect to be more representative of the true population of exoplanets in terms of their orbital characteristics, with smaller planet sizes, longer orbital periods and a more uniform spread of orbital inclinations. Current detection methods still favor larger planets closer to their stars, because they are the easiest to find. The current catalog of known exoplanets is not entirely representative of the wider population of exoplanets out there. (Transiting exoplanets cross their host stars' faces from our perspective on Earth.) ![]() "The 53 nHz value is for all the planets that we currently know, but it contains some biases that are making the value higher, because transiting exoplanets have a higher drift rate than non-transiting exoplanets, and bigger exoplanets have bigger drift rates than smaller exoplanets," Li told in a telephone interview. Related: The 10 most Earth-like exoplanets There's even scope to reduce it much further, study team members said. And being a lower value than plus or minus 200 nHz, it will reduce the amount of computational resources required and speed up the search. This new result is more accurate because it measures the drift rate at all points in an exoplanet's orbit, not just at those points that maximize the drift rate. This means that, for 99% of planetary systems, the frequency of a signal detected from a distant exoplanet would be expected to drift in frequency at a maximum rate of plus or minus 53 nHz. Now, by modeling about 5,300 real exoplanets, a team led by graduate student Megan Li of the University of California, Los Angeles was able to refine and reduce the maximum value for the drift rate caused by the orbital motion of exoplanets to plus or minus 53 nHz. Using plus or minus 200 nHz as a maximum drift rate requires increased computational resources, slowing down the speed with which data from SETI searches is analyzed. However, while astronomers do not always know how fast exoplanets are spinning - the exception is tidally locked planets, which have a day that is the same length as their year - they can measure an exoplanet's orbital period and derive a maximum frequency drift from this figure. ![]() These shifts can be accounted for when analyzing signals. Radio astronomers know that Earth's orbital motion causes a drift rate of 0.019 nanoHertz (nHz) and that Earth's spinning on its axis creates an additional 0.1 nHz drift. (Think of how the sound of a police or ambulance siren changes as it approaches and then passes you.)īoth the orbital motion and the daily rotation of an exoplanet, plus Earth's own orbital motion and daily rotation, contribute to the frequency drift of any signal that may be transmitted from the exoplanet and received here on Earth. This results in the signal appearing to "drift" across a range of frequencies as the transmitter moves. If the transmitter is moving away from us, the wavelength becomes stretched and the frequency decreases if it's moving towards us, the wavelength shortens and and the frequency increases. A Doppler shift is the lengthening or shortening of the frequency of a signal caused by the motion of the transmitter.
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