Radio signal detected for the first time from a planet outside our solar system

NASA/ESA/CSA/STScI/Ralf Crawford (STScI)

Astronomers say they have directly detected the first-ever radio emission from a planet outside the solar system. The signal, however, is evidence of a colossal magnetic field — not intelligent life.

“I know radio signals are associated with searches for extraterrestrial intelligence,” said Edo Berger, a professor of astronomy at Harvard University. “But this is something very different.”

The discovery, described in a new paper awaiting publication in a peer-reviewed journal, traces repeating radio bursts that appear to come from the exoplanet Beta Pictoris b, located 63 light-years from Earth — a short distance, astronomically speaking. The gas giant, about 12 times the mass of Jupiter, is one of three planets orbiting a young star that is 1.75 times as massive as the sun.

Processes associated with the planet’s magnetic field produce the radio emission, according to Berger, a researcher at the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts. Specifically, the detection involves auroras similar to Earth’s northern lights — the spectacular displays sparked by magnetic storms involving charged particles from the sun. “In order to see radio waves that extend all the way to the frequencies that we observed, you need an incredibly strong magnetic field,” added Berger, a coauthor of the paper posted September 15 to the preprint platform ArXiv.

New evidence deepens mystery of moon’s ancient magnetic field

Not all planets have a magnetic field. Those that have one benefit from a natural shield that deflects disruptive energy. Earth’s magnetic field, for example, protects our atmosphere from being stripped away by solar wind , a continuous outflow of plasma that contains charged particles like protons and electrons.

“The magnetic field on this planet is at least 200 times stronger than the magnetic field of Jupiter,” Berger said, referring to Beta Pictoris b. Jupiter’s magnetic field, according to NASA , is powerful enough to generate a magnetosphere — the region of space influenced by the magnetic field — that ranks as the largest structure in our solar system, stretching up to 2 million miles (3 million kilometers) toward the sun.

Jupiter’s field also creates striking auroras , when electrically charged particles spewed from volcanoes on its moon Io become trapped around the field’s poles. As the gas giant rotates, the charged particles emit a glow but also a radio signal. “As these very high-energy particles are spiraling inside the magnetic field, along with the aurora they also produce radio waves,” Berger said.

NASA/JPL-Caltech/SwRI

Mystery of Jupiter’s northern lights solved after 40 years, scientists say

Astronomers call this type of signal an auroral radio emission. The phenomenon has been previously observed from Jupiter, Saturn and the sun, as well as stars outside the solar system and cool objects known as brown dwarfs — an intermediate between a star and a planet. This type of signal is what Berger and his colleagues detected from Beta Pictoris b, which ultimately points to the presence of an intense magnetic field that’s causing auroras and the radio emission.

Magnetic fields have implications for the structure of exoplanets and their atmospheres, according to Berger. “Radio observations can give us a completely new view on planets beyond our system,” he said.

There had been hints of radio emissions from exoplanets before, but none had been confirmed, largely because it couldn’t be ruled out that the source was actually the host star, said Joseph Callingham, an associate professor at the Anton Pannekoek Institute for Astronomy of the University of Amsterdam in the Netherlands.

“What is unique for this study is that they localise the emission to the planet itself, separate from the star,” Callingham, who was not involved in the new research, wrote in an email.

The Beta Pictoris system is astronomically very young at about 23 million years old compared with our own solar system’s age of 4.5 billion years. Beta Pictoris b — the planet from which the radio signal potentially originates — was discovered in 2008 . Two additional planets, Beta Pictoris c and Beta Pictoris d, were discovered in 2019 and 2026 , respectively.

The planetary system is among the most studied in our galaxy, and its star is known to host 30 orbiting comets and a giant disk of dust and debris, which NASA’s Hubble Space Telescope photographed in detail in 2015. Some of the debris swirling in the rotating disk is a remnant from planetary formation.

NASA/ESA/D. Apai and G. Schneider (University of Arizona)

The researchers used MeerKAT , an array of 64 radio telescope dishes in South Africa, to detect the signal, but they were highly surprised to see it coming from such a well-observed set of celestial bodies, Berger said. “My graduate student Kevin was going through the data. He came into my office one day with the detection and he said, ‘I don’t think you’re going to believe this,’” Berger recalled, referring to lead study author Kevin Ortiz Ceballos, a doctoral researcher at the Center for Astrophysics | Harvard & Smithsonian. “This was really unexpected for us. We were doing the survey as a bit of a fishing expedition, knowing that we would only detect sources if the magnetic field was incredibly strong.”

The surprise stems from the fact that astronomers had assumed, according to Berger, that if exoplanets have magnetic fields, they should look roughly like Jupiter’s, and therefore their radio emissions would be at lower frequencies than what he and his colleagues found. Detecting the signal was the result of “going against the perceived wisdom in the field,” he said.

However, the researchers noted the report has not yet undergone peer review, the process in which independent experts assess a research paper before publication in a scientific journal. The review is underway and will be completed over the next few months.

Berger said he is confident about the quality of the detection. The research team pinpointed the radio emission’s source as Beta Pictoris b, ruling out an initial suspicion that it could be coming from the star instead. “We recorded it multiple times, at multiple frequencies. It’s there every single time,” he said.

Scientists who were not involved with the new research urged caution when interpreting the findings.

If the discovery holds up under the scrutiny of peer review, it would represent an incredibly exciting and key step forward in understanding the behavior of worlds beyond our solar system, according to Jonathan Nichols, a professor in planetary auroras at the University of Leicester in England. “Auroral radio emissions are important because they allow us to understand how an object interacts with its local space environment,” he wrote in an email.

Alice Kitterman/National Science Foundation

Repeating radio signal leads astronomers to an Earth-size exoplanet

“They allow us to infer properties of the planet that we cannot otherwise measure,” Nichols explained, referring to auroras, “and, importantly, they enable us to test theories and ideas developed for our own solar system in more extreme conditions.”

If confirmed, the results would show that exoplanets can have much stronger magnetic fields than expected, which would be a crucial learning, according to Callingham of the University of Amsterdam.

The authors have requested more telescope time to further study Beta Pictoris b and perhaps unlock some of its puzzles, such as why the planet’s magnetic field is so strong. “I think that’s going to be a question that occupies people for a while,” Berger said.

NASA/ESA/CSA/STScI/Ralf Crawford (STScI)

天文学家称，他们首次直接探测到来自太阳系外行星的射电辐射。然而，该信号表明该行星存在巨大的磁场，而非智慧生命。

“我知道无线电信号与搜寻地外文明有关，”哈佛大学天文学教授埃多·伯杰说，“但这完全是两回事。”

这项发现已发表在一篇等待同行评审期刊刊登的新论文中，论文追踪到重复出现的射电暴，这些射电暴似乎来自系外行星绘架座β星b，该行星距离地球63光年——从天文尺度来看，这算是很近的距离。这颗气态巨行星的质量约为木星的12倍，是围绕一颗年轻恒星运行的三颗行星之一，这颗恒星的质量约为太阳的1.75倍。

据位于马萨诸塞州剑桥市的哈佛-史密森天体物理中心的研究员伯杰（Berger）称，与行星磁场相关的过程产生了无线电辐射。具体来说，探测到的现象与地球北极光类似——这种壮观的景象是由太阳带电粒子引发的磁暴造成的。“为了观测到我们观测到的频率范围内的无线电波，你需要一个极其强大的磁场，”伯杰补充道。他是9月15日发表在预印本平台arXiv上的论文的合著者之一。

新证据加深了月球远古磁场的神秘感

并非所有行星都拥有磁场。拥有磁场的行星受益于这层天然屏障，能够偏转有害能量。例如，地球磁场保护着我们的大气层免受太阳风的侵蚀。太阳风是一种持续不断的等离子体外流，其中包含质子和电子等带电粒子。

“这颗行星上的磁场强度至少是木星磁场的 200 倍，”伯杰说，他指的是绘架座β星 b。据美国宇航局称，木星的磁场非常强大，足以产生磁层——受磁场影响的空间区域——它是我们太阳系中最大的结构，向太阳方向延伸达 200 万英里（300 万公里）。

木星磁场还会形成壮观的极光，这是由于木卫一（伊奥）上的火山喷发的带电粒子被磁场两极捕获所致。随着这颗气态巨行星的自转，这些带电粒子不仅会发出光芒，还会产生无线电信号。“这些高能粒子在磁场中螺旋运动时，除了极光之外，还会产生无线电波，”伯杰说道。

NASA/JPL-加州理工学院/西南研究院

科学家称，木星北极光之谜历经40年终于解开。

天文学家将这种信号称为极光射电辐射。此前，人们已在木星、土星和太阳，以及太阳系外的恒星和被称为褐矮星的低温天体（介于恒星和行星之间的天体）上观测到这种现象。伯杰和他的同事在绘架座β星b上探测到的正是这种信号，这最终表明该天体存在一个强磁场，正是这个磁场导致了极光和射电辐射。

伯杰表示，磁场对系外行星的结构及其大气层有着重要影响。“射电观测可以为我们提供关于太阳系外行星的全新视角，”他说。

荷兰阿姆斯特丹大学安东·潘内库克天文研究所副教授约瑟夫·卡林厄姆表示，此前曾有迹象表明系外行星会发出无线电辐射，但都没有得到证实，这主要是因为无法排除辐射源实际上是宿主恒星的可能性。

“这项研究的独特之处在于，他们将辐射源定位到行星本身，而不是恒星，”卡林厄姆（他并未参与这项新研究）在一封电子邮件中写道。

与太阳系45亿年的年龄相比，绘架座β星系在天文学上非常年轻，年龄约为2300万年。2008年，人们发现了绘架座β星b——这颗行星可能就是无线电信号的来源。另外两颗行星，绘架座β星c和绘架座β星d，分别于2019年和2026年被发现。

这个行星系统是银河系中研究最多的系统之一，其恒星周围已知有 30 颗彗星和一个巨大的尘埃碎片盘，NASA 的哈勃太空望远镜在 2015 年对其进行了详细拍摄。旋转圆盘中旋转的一些碎片是行星形成时的遗迹。

美国宇航局/欧空局/D。 Apai 和 G. Schneider（亚利桑那大学）

研究人员利用位于南非的MeerKAT射电望远镜阵列（由64个射电望远镜组成）探测到了这个信号，但他们非常惊讶地发现信号竟然来自一组观测非常充分的天体，伯杰说。“我的研究生凯文当时正在分析数据。有一天他拿着探测结果来到我的办公室，说：‘我觉得你不会相信的，’”伯杰回忆道，他指的是该研究的主要作者、哈佛-史密森天体物理中心的博士研究员凯文·奥尔蒂斯·塞瓦洛斯。“这真的出乎我们的意料。我们当时只是抱着试试看的态度进行这项观测，因为我们知道只有磁场极其强烈的天体才能被探测到。”

伯杰表示，这一发现令人惊讶之处在于，天文学家此前一直认为，如果系外行星拥有磁场，它们应该与木星的磁场大致相似，因此它们的无线电辐射频率应该低于他和同事们发现的频率。他说，探测到这一信号是“与该领域普遍认知相悖”的结果。

然而，研究人员指出，该报告尚未经过同行评审，即由独立专家在科学期刊发表前对研究论文进行评估的过程。评审工作正在进行中，将在未来几个月内完成。

伯杰表示他对探测结果的质量充满信心。研究团队将射电辐射的来源确定为绘架座β星b，排除了最初认为辐射可能来自恒星的猜测。“我们在多个频率上多次记录到它，每次都存在，”他说。

未参与这项新研究的科学家们敦促在解读研究结果时要谨慎。

英国莱斯特大学行星极光教授乔纳森·尼科尔斯表示，如果这项发现经得起同行评审的检验，那将是理解太阳系外天体行为的一个令人无比兴奋的关键性进展。他在一封电子邮件中写道：“极光无线电辐射非常重要，因为它们使我们能够了解天体如何与其周围空间环境相互作用。”

爱丽丝·基特曼/美国国家科学基金会

重复的无线电信号引导天文学家发现了一颗地球大小的系外行星

尼科尔斯解释说：“它们使我们能够推断出我们无法以其他方式测量的行星特性，”他指的是极光，“而且，更重要的是，它们使我们能够在更极端的条件下检验为我们自己的太阳系开发的理论和想法。”

阿姆斯特丹大学的卡林厄姆表示，如果得到证实，结果将表明系外行星的磁场可能比预期的要强得多，这将是一项至关重要的发现。

作者们已申请更多望远镜观测时间，以便进一步研究绘架座β星b，并可能解开它的一些谜团，例如这颗行星的磁场为何如此之强。“我认为这个问题将会持续一段时间，”伯杰说。