What does a stressed plant sound like? A bit like bubble-wrap being popped. Researchers in Israel report in the journal Cell on March 30 that tomato and tobacco plants that are stressed—from dehydration or having their stems severed—emit sounds that are comparable in volume to normal human conversation. The frequency of these noises is too high for our ears to detect, but they can probably be heard by insects, other mammals, and possibly other plants.

“Even in a quiet field, there are actually sounds that we don’t hear, and those sounds carry information,” says senior author Lilach Hadany, an evolutionary biologist and theoretician at Tel Aviv University. “There are animals that can hear these sounds, so there is the possibility that a lot of acoustic interaction is occurring.”

Although ultrasonic vibrations have been recorded from plants before, this is the first evidence that they are airborne, a fact that makes them more relevant for other organisms in the environment. “Plants interact with insects and other animals all the time, and many of these organisms use sound for communication, so it would be very suboptimal for plants to not use sound at all,” says Hadany.

The researchers used microphones to record healthy and stressed tomato and tobacco plants, first in a soundproofed acoustic chamber and then in a noisier greenhouse environment. They stressed the plants via two methods: by not watering them for several days and by cutting their stems. After recording the plants, the researchers trained a machine-learning algorithm to differentiate between unstressed plants, thirsty plants, and cut plants.

The team found that stressed plants emit more sounds than unstressed plants. The plant sounds resemble pops or clicks, and a single stressed plant emits around 30–50 of these clicks per hour at seemingly random intervals, but unstressed plants emit far fewer sounds. “When tomatoes are not stressed at all, they are very quiet,” says Hadany.

Water-stressed plants began emitting noises before they were visibly dehydrated, and the frequency of sounds peaked after five days with no water before decreasing again as the plants dried up completely. The types of sound emitted differed with the cause of stress. The machine-learning algorithm was able to accurately differentiate between dehydration and stress from cutting and could also discern whether the sounds came from a tomato or tobacco plant.

Although the study focused on tomato and tobacco plants because of their ease to grow and standardize in the laboratory, the research team also recorded a variety of other plant species. “We found that many plants—corn, wheat, grape, and cactus plants, for example—emit sounds when they are stressed,” says Hadany.

The exact mechanism behind these noises is unclear, but the researchers suggest that it might be due to the formation and bursting of air bubbles in the plant’s vascular system, a process called cavitation.

Whether or not the plants are producing these sounds in order to communicate with other organisms is also unclear, but the fact that these sounds exist has big ecological and evolutionary implications. “It’s possible that other organisms could have evolved to hear and respond to these sounds,” says Hadany. “For example, a moth that intends to lay eggs on a plant or an animal that intends to eat a plant could use the sounds to help guide their decision.”

Other plants could also be listening in and benefiting from the sounds. We know from previous research that plants can respond to sounds and vibrations: Hadany and several other members of the team previously showed that plants increase the concentration of sugar in their nectar when they “hear” the sounds made by pollinators, and other studies have shown that plants change their gene expression in response to sounds. “If other plants have information about stress before it actually occurs, they could prepare,” says Hadany.

Sound recordings of plants could be used in agricultural irrigation systems to monitor crop hydration status and help distribute water more efficiently, the authors say.

“We know that there’s a lot of ultrasound out there—every time you use a microphone, you find that a lot of stuff produces sounds that we humans cannot hear—but the fact that plants are making these sounds opens a whole new avenue of opportunities for communication, eavesdropping, and exploitation of these sounds,” says co-senior author Yossi Yovel, a neuro-ecologist at Tel Aviv University.

“So now that we know that plants do emit sounds, the next question is—’who might be listening?'” says Hadany. “We are currently investigating the responses of other organisms, both animals and plants, to these sounds, and we’re also exploring our ability to identify and interpret the sounds in completely natural environments.”

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How to see 5 planets

This week (late March 2023), you can see five planets lined up in our evening sky: Venus and Uranus, Jupiter and Mercury and Mars. Gianluca Massi of the Virtual Telescope Project in Rome, Italy, showed them through a telescope earlier today (March 29). To enjoy his presentation, watch the video below. In addition, you can see them in the sky, perhaps, if your sky conditions are very good, and you have a sharp eye.

As soon as the sun sets, the planets are positioned in a gentle arc across the evening sky, following the sun’s path across our sky. Likewise, the Moon and the planets also follow the eclipse.

How can we see the planets? Go out around sunset and look west. Among them you can easily spot the bright planet Venus.

Then use binoculars to scan the planet Uranus next to Venus.

Then aim your binoculars low in the sky, near the point where the sun is setting. That is where you will find Jupiter and Mercury.

Then look high in the sky — still see the eclipse or the path of the Sun — to Mars.

 

Guide to Planetary Viewing

Venus and Uranus. Of these five planets, Venus is the brightest and Uranus is the dim. These two are close together in the sky. Venus is easily visible to the eye. It is the first “star” (actually, planet) to come into view. Uranus shines at +5.8 magnitudes. This is theoretically obvious. But, in practice, you need a dark sky and a telescope to find it. It was roughly 1.5 degrees or three moon widths from Venus earlier this week. Uranus will be closest to Venus on Thursday, March 30.

Thursday and Wednesday. Jupiter is the 2nd brightest planet. But it is now near sunset and visible only in bright twilight. Bright twilight skies make Jupiter more difficult to find. But Jupiter is still visible to the naked eye very close to sunset. And Wednesday? It is fainter than Jupiter (though still brighter than most stars). But it is near sunset. Shortly after sunset, start looking for the pair on the western horizon. You need clear skies and an unobstructed western view to catch them. A telescope should help. They disappear only 30 minutes after sunset. So, when the sun sets, the clock chimes.

tuesday, now the 5th planet in the evening sky, was easy to spot earlier this week because it’s not far from the Moon in our sky’s dome. A bright red light near the moon on Tuesday evening, March 28, 2023. Mars is bright. It is brighter than most stars. And it is clearly red. Even after the sun goes away, you can still spot Mars by its color and by the fact that it doesn’t shine like stars.

Some inventor charts

Bottom line: You have a chance to see five planets tonight and throughout this week. Here are illustrations and information, including where to look in the video.

For more celestial events, visit EarthSky’s Night Sky Guide.

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Boeing’s debut Starliner spacecraft launch carrying its first-ever crew of astronauts to the International Space Station is being postponed again, and is not expected to fly until 21 July at the earliest.

Steve Stich, manager of Commercial Crew Program at NASA, confirmed the delay in a media teleconference on Wednesday. Officials from the space agency and Boeing need more time to assess the capsule, and to avoid conflicts with upcoming flights scheduled to the ISS.

Boeing’s Crew Flight Test (CFT) mission has suffered repeated setbacks, and was originally slated to fly in April. “We’ve deliberated and decided that the best launch attempt is no earlier than July 21st,” Stitch said.

“Where we’re at right now is really getting through the certification work… it is a large amount of work which has been going on for well over a year. There’s 600 components that have to be qualified on the Starliner for NASA and Boeing to review jointly [and] over 70 hazard reports. And then a total of what we call 370 verifications,” he added.

They are both paying close attention to the parachute system on the Starliner deployed to land the spacecraft safely back on Earth. Ground tests will examine the parachute’s ability to launch properly and slow the Starliner to splash down safely for the return of astronauts Butch Wilmore and Suni Williams, who will fly and spend eight days docked to the ISS in the CFT.

Joel Montalbano, manager of  NASA’s International Space Station Program, said that activities onboard the ISS are jam packed over the next few months. The Soyuz MS-23 currently docked to the space station will be relocated to another module. Russian cosmonauts and American astronauts will also be performing separate spacewalks to adjust for incoming solar arrays and retrieve hardware.

There are also upcoming cargo deliveries as well as the Axiom-2 mission, the second private crewed mission to the ISS, which will send the first Saudi Arabian woman, Rayyanah Barnawi, to space. Barnawi’s crewmates include Ali Alqarni, a second Saudi representative, Peggy Whitson, a NASA veteran, and John Shoffner, an investor and pilot.

All that means is Boeing will have to find a flight slot after these events.

“We’re very close,” said Mark Nappi, vice president and program manager of the CST Starliner at Boeing. He said the company was working hard to inspect the spacecraft’s hardware, build the service module, refurbish the crew module, and verify its flight software.

“Most of the areas that needed to be completed are going to be completed by the end of April. In the one area that Steve talked about, which is the parachute, the verification closure notice and the hazard report will poke out into May,” he said.

The next major milestone will be loading the propellant into the spacecraft about 40 days prior to its launch. ®

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