天体物理学家发布了系外彗星带及其内部“鹅卵石”的图像。系外彗星是太阳系外的岩石和冰块，尺寸至少1公里。这些彗星带存在于至少20%的行星系统中。研究显示，这些彗星带的形状多样，有些是圆盘状，有些是窄环状，甚至有些是偏心的多环结构。这些结构暗示着未被探测到的行星的存在，它们的引力影响着系统中鹅卵石的分布。研究还发现，随着行星系统的老化，鹅卵石数量减少，尤其是在靠近中心恒星的区域。此外，通过彗星带的垂直厚度，间接推断出这些带中可能存在140公里到月球大小的物体。

☄️ 系外彗星带是由岩石和冰块组成的，存在于至少20%的行星系统中，这些彗星带的形状各异，包括圆盘状、窄环状以及偏心的多环结构。

🪐 彗星带的结构多样性暗示着未被探测到的行星的存在，这些行星的引力影响着系统中鹅卵石的分布，导致了彗星带的不同形状和结构。

⏳ 研究发现，随着行星系统的老化，彗星带内的鹅卵石数量会减少，尤其是在靠近中心恒星的区域，这种减少趋势更加明显。

🔭 通过彗星带的垂直厚度，间接推断出这些带中可能存在140公里到月球大小的物体，揭示了行星系统中隐藏的巨大天体。

Astrophysicists have released a series of images of exocomet belts and the tiny “pebbles” that reside in them.

Exocomets are boulders of rock and ice, at least 1 km in size, that exist outside our solar system. Exocometary belts – regions containing many such icy bodies – are found in at least 20% of planetary systems. When the exocomets within these belts smash together they can also produce small pebbles.

The belts in the latest study orbit 74 nearby stars that cover a range of ages – from those that are have just formed to those in more mature systems like our own Solar System. The belts typically lie tens to hundreds of astronomical units (the distance from the Earth to the Sun) from their central star.

At that distance, the temperature is between -250 to -150 degrees Celsius, meaning that most compounds on the exocomets are frozen as ice.

While most exocometary belts in the latest study are disks, some are narrow rings. Some even have multiple rings/disks that are eccentric, which provides evidence that yet undetectable planets are present and their gravity affects the distribution of the pebbles in these systems.

According the Sebastián Marino from the University of Exeter, the images reveal “a remarkable diversity in the structure” of the belts.

Indeed, Luca Matrà from Trinity College Dublin says that the “power” of such a large survey is to reveal population-wide properties and trends. “[The survey] confirmed that the number of pebbles decreases for older planetary systems as belts run out of larger exocomets smashing together, but showed for the first time that this decrease in pebbles is faster if the belt is closer to the central star,” Matrà adds. “It also indirectly showed – through the belts’ vertical thickness – that unobservable objects as large as 140 km to Moon-size are likely present in these belts.”

The researchers took the images using the Atacama Large Millimeter/submillimeter Array – an array of 66 radio telescopes in the Atacama Desert of northern Chile – as well as the eight-element Submillimeter Array based in Hawaii.

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