We present evidence that excesses in Be in polluted white dwarfs (WDs) are the result of accretion of icy exomoons that formed in the radiation belts of giant exoplanets. Here we use excess Be in the white dwarf GALEX J2339–0424 as an example. We constrain the parent body abundances of rock-forming elements in GALEX J2339–0424 and show that the overabundance of beryllium in this WD cannot be accounted for by differences in diffusive fluxes through the WD outer envelope nor by chemical fractionations during typical rock-forming processes. We argue instead that the Be was produced by energetic proton irradiation of ice mixed with rock. We demonstrate that the MeV proton fluence required to form the high Be/O ratio in the accreted parent body is consistent with irradiation of ice in the rings of a giant planet within its radiation belt, followed by accretion of the ices to form a moon that is later accreted by the WD. The icy moons of Saturn serve as useful analogs. Our results provide an estimate of spallogenic nuclide excesses in icy moons formed by rings around giant planets in general, including those in the solar system. While excesses in Be have been detected in two polluted WDs to date, including the WD described here, we predict that excesses in the other spallogenic elements Li and B, although more difficult to detect, should also be observed, and that such detections would also indicate pollution by icy exomoons formed in the ring systems of giant planets.

我们提供的证据表明，被污染的白矮星（WDs）中的Be过量是结冰系外显子积聚的结果，这些结冰外显子形成于巨大系外行星的辐射带中。这里我们以白矮星GALEX J2339–0424中多余的Be为例。我们在GALEX J2339–0424中限制了成岩元素的母体丰度，并表明该WD中铍的丰度无法通过WD外部包络的扩散通量差异或典型的成岩过程中的化学分馏来解释。 。相反，我们认为Be是由高能质子辐照冰与岩石混合产生的。我们证明在吸积的母体中形成高Be / O比所需的MeV质子通量与辐射带内一个巨大行星的环中的冰辐射一致，随后积聚冰块，形成月亮，随后由WD积聚。土星的冰冷卫星可作为有用的类似物。我们的结果提供了一个估算，即通常由巨型行星（包括太阳系中的行星）周围的环形成的冰月形卫星中的崩解性核素过量。尽管迄今为止已经在两个受污染的WD中检测到了Be的过量，包括此处所述的WD，但我们预测，虽然更难检测，但也应观察到其他散裂性元素Li和B中的过量，并且这种检测也将表示由巨型行星环系统中形成的冰冷外显子污染。我们的结果提供了一个估算，即通常由巨型行星（包括太阳系中的行星）周围的环形成的冰月形卫星中的崩解性核素过量。尽管迄今为止已经在两个受污染的WD中检测到了Be的过量，包括此处所述的WD，但我们预测，虽然更难检测，但也应观察到其他散裂性元素Li和B中的过量，并且这种检测也将表示由巨型行星环系统中形成的冰冷外显子污染。我们的结果提供了一个估算，即通常由巨型行星（包括太阳系中的行星）周围的环形成的冰月形卫星中的崩解性核素过量。尽管迄今为止已经在两个受污染的WD中检测到了Be的过量，包括此处所述的WD，但我们预测，虽然更难检测，但也应观察到其他散裂性元素Li和B中的过量，并且这种检测也将表示由巨型行星环系统中形成的冰冷外显子污染。