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recent data released from the Gaia mission

to map the Milky Way Galaxy, Reinhold et

al. meticulously selected solar-like stars with

reliable periods and measured their photo-

metric variability. This sample of stars rep-

resents the largest number of solar-like stars

with the closest properties to those of the

Sun identified to date. For the Sun, the au-

thors used data from the VI RGO (Variability

of Solar Irradiance and Gravity Oscillations)

experiment. The authors established that the

magnetic activity level of the Sun, based on

photometric variability, is lower than that

of the solar-like stars. But why does the Sun

seem to differ so much from other stars that

appear to be the most similar to it? Are the

data telling us that the Sun can reach higher

activity levels?

The notion that the Sun might reach

higher solar activity levels is quite unpleas-

ant news for technological societies. The

Sun’s strong activity and the associated so-

lar storms not only produce the beautiful

northern and southern lights but also might

compromise satellites and power lines,

threaten the lives of astronauts in space,

and affect Earth’s climate. High stellar ac-

tivity also has a non-negligible impact on

the habitability of planets found around ac-

tive stars because their atmospheres might

be swept out into deep space by such high

magnetic activity. Thus, characterizing stel-

lar magnetic properties is also extremely

important for exoplanet research.

These results also question the theory of

a transitioning Sun. Astronomers thought

that, as stars evolve, they gradually slow

down (the rotation period grows longer) and

become less active ( 5 ). Recent studies have

suggested, however, that at a given point in

its lifetime, the star faces a dramatic midlife

crisis: It s activity cycle shuts down, and the

star’s rotation stops slowing down ( 6 , 7 ). Ac-

cording to this scenario, the Sun is approach-

ing that time of its life. Can the Sun already

be transitioning, while the solar-like stars

observed with Kepler in the new study con-

tinue to progress in their steady evolution?

The future of our Sun remains uncertain.

The Kepler mission unexpectedly revolution-

ized stellar physics and, with new discover-

ies, challenged what we thought we knew.

Six years after the conclusion of its main mis-

sion, the legacy of Kepler data continues to

yield noteworthy information, as shown by

Reinhold et al. The current TE SS (Transiting

Exoplanet Survey Satellite) and future PL ATO

(Planetary Transits and Oscillations of stars)

space missions, while searching the full sky for

exoplanets, will collect data for an extraordi-

nary number of stars. However, these missions

are planned to obtain short-term observations,

which will hamper a proper characterization

of stellar magnetic activity.

On the bright side, these missions will ob-

serve br ighter stars than Kepler did. This will

allow astronomers to do ground-based follow-

up observations, which will provide indepen-

dent constraints on stellar activity. This was

not possible for most Kepler targets, which

are faint. Future research will certainly pro-

vide answers to some of the open questions on

rotation and magnetic evolution and, in turn,

stellar evolution itself. j

REFERENCES AND NOTES

1. T. Reinhold et al., Science 368 , 518 (2020).


2. D. H. Hathaway, Living Rev. Sol. Phys. 12 , 4 (2015).


3. A. R. G. Santos et al., Astrophys. J. Suppl. Ser. 244 , 21
   (2019).


4. S. Mathur et al., Astron. Astrophys. 562 , A124 (2014).


5. A. Skumanich, Astrophys. J. 171 , 565 (1972).


6. J. L. van Saders et al., Nature 529 , 181 (2016).


7. T. S. Metcalfe et al., Astrophys. J. 826 , L2 (2016).

ACKNOWLEDGMENTS

The authors are supported by grants from NASA

(NNX17AF27G) and the Spanish Ministry (RYC-2015-17697).

10.1126/science.abb9208

VIRGO data

Kepler data

Solar Dux

Time

Stellar Dux

Time

~ Rotation period

~ Rotation period

~ Max. amplitude

~ Max. amplitude

CANCER

Profiling

prostate biology

Prostate luminal secretory

cells can function as

facultative stem cells

By Kathleen Kelly

M

olecular profiling of heterogeneous

cell populations at the single-cell

level using single-cell RNA sequenc-

ing (scRNA-seq) has provided re-

fined cell type–specific gene expres-

sion signatures and allowed the

discovery of rare cell types. Applying such

an approach in the context of anatomy and

pathology informs disease mechanisms. A

requirement for androgen is a cardinal fea-

ture in the development and maintenance

of normal prostate and for the maintenance

of prostate adenocarcinoma ( 1 ). On page 497

of this issue, Karthaus et al. ( 2 ) provide an

in-depth characterization of prostatic cellu-

lar heterogeneity and address mechanisms

of androgen independence in regenerating

mouse prostates. They identify an adaptive

stemlike phenotype in a large population of

secretory epithelial cells undergoing andro-

gen-dependent regeneration, uncovering an

unappreciated plasticity in these differenti-

ated cells, which has implications for pros-

tate cancer therapy.

Prostate epithelium consists of three pri-

mary cell types: luminal cells, an underlying

layer of basal cells, and rare neuropeptide-

secreting neuroendocrine cells. Luminal cells

express the androgen receptor (AR) tran-

scription factor and are thought to be the

main cell of origin for prostate cancer ( 3 ).

To better understand the potential of lumi-

nal cells as targets of genetic alteration and

transformation, much attention has focused

on their self-renewal characteristics.

In rodents, androgen withdrawal by castra-

tion results in the death of ~90% of luminal

cells, and androgen readministration fully

regenerates the prostate within a month.

Similarly, normal human prostates regress in

size and cellularity after androgen depriva-

tion. Using lineage tracing, whereby selected

cells and their progeny can be specifically

visualized, luminal cells in adult mice were

shown to derive from luminal progenitor

Laboratory of Genitourinary Cancer Pathogenesis,

Center for Cancer Research, National Cancer Institute,

National Institutes of Health, Bethesda, MD, USA.

Email: [email protected]

1 MAY 2020 • VOL 368 ISSUE 6490 467

Star light, star bright

Dark magnetic spots are a manifestation of stellar activity. As the star rotates, spots modulate stellar

brightness, revealing stellar rotation and magnetic properties. The amplitude of spot modulation is

proportional to the area of the Sun or star covered by spots. Data from the VIRGO instrument and Kepler

satellite show that stars with solar-like properties are typically more active than the Sun.